

51 

(pic's 



j 





ii ii'ii mil ii li ill 
II 



iijiniinii 

003 537 161 8 







Hollinger Corp. 
pH 8.5 







A COURSE 


QB 51 






.M665 






Copy 1 




OF 



SIX LECTURES 



ON 



ASTRONOMY, 



DELIVERED IN THE CITY OF NEW-YORK 



BY 



PROF. oTm. MITCHELL. 



SPECIALLY REPORTED FOR THE NEW-YORK TRIBUNE. 



NEW-YORK : 

GREELEY & McELRATH, TRIBUNE BUILDINGS. 

1848. 



These Lectures were delivered at the Broadway Tab.ernacle in the City of New-York in the 
month of December, 1847, by Professor O. M. Mitchell of Cincinnati, Ohio, one of the most eminent 
Astronomers in the world, and a scholar of whom America may justly be proud. Traveling eastward on 
business connected with Science, he was met at this City by an invitation from a number of our most 
eminent citizens, to favor them with a Course of Lectures on the sublime Science to which he has de- 
voted his life. The time allowed him was brief, and the course and matter of the Lectures necessarily 
more condensed than he could have wished. Brief as they are, however, they will be found of great 
interest and value to the general reader, to whom the cabalistic arcana of this beautiful Science is 
seldom opened and rarely so intelligibly explained. The great inquiry for The Tribune, (for which 
paper they were specially reported) containing these Lectures, has induced the publishers to issue them 
in the present collected form that they may at all times be accessible to the reading community. 

Tribune Office, New-York, Dec. 1847, 



tJ.8.fceo 






ASTRONOMY 1 . 



. LECTURE L 



c««a f t. n fPmf Dsvies introducinff Prof. Mitchell.... A Survey of the Heavens.... The Problem of the Universe 
Rm vbl^"lTi{otion-^{&nl^j-0{ Centrifugal Force.... The Earth's Revolution.... Influence of the 
Moon upon the Earth.... Perturbations Calculated.... Eclipses, Past and Future Determined.... Comets -Re- 
mi™ nf a Cornet now expected ..The Fixed Stars.... Measurement of the Distance to the Moon.... Of the 
Fixed [Stars— The Immensity of their Distance from us. ...The Nebulae.... Present State of Astronomical Ob 
servations at Cincinnati. 



A lsrge and respectable audience assembled on Wed- 
nesday evening.Dec. 1 , 1847, at the Broadway Tabernacle on 
the occasion of the delivery of the first of a Course of Six 
Lectures on Astronomy to be given by the learned and 
eloquent Professor Mitchell of Cincinnati. The lec- 
turer was introduced to the audience by Prof. Charles 
Davies, in the following remarks : 

Ladies and Gentlemen : It is little more than twenty 
years since a Professor of Mathematics in our Military 
Academy was struck with the initiatory examination of a 
young lad from an interior town in Ohio, on the occasion of 
his presenting himself for admission into that Institution. 
He passed regularly through the various classes, received 
the first honors, and was retained two years after he grad- 
uated as an assistant in departments of Science. A tew 
years since, that Professor had occasion to visit the \\ e st- 
ern country, and he stopped for a few days at Cincinnati— 
a beautiful city on one of the banks of the Ohio, encir- 
cled by a series of hills which form a most perfect amphi- 
theatre. The day after his arrival he received a call from 
his early fri»ndand pupil, and, after the first salutation 
incident to the meeting of old friends who had been long 
separated frcm each other, ha received an invitation to 
visit the Observatory. " What ! " said he, " an Observatory 
in this new region of the world ?— before the forest 
tree* and stumps are fairly cleared away?" 'Cer- 
tainly," was the reply ; " such a one as you will he 
delighted to visit: which I hope you will do to-morrow 
evening, if the weather be fair and the skies auspicious." 
In the meantime that Professor having some curiosity in 
regard to this Observatory, learned through his friends 
that his young punil— fired with the live of Science— oa 
his return to his native State, had conceived the noble pro- 
ject of establishing: at Cincinnati— the Queen City of the 
West— a permanent institution for the cultivation and dif- 
fusion of Astronomical Science. He learned, farther, that 
through his own individual efforts, aided by the strong 
feeling which he had excited in the inhabitants of that 
city for the promotionof this object, he had been enabled to 
realize a sufficient sum, which had been sent to Europe for 
the purchase of instruments; and he had, in fact, caused 
an Observatory to be erected on one of the neighboring 
hills, vying in excellence with similar structures in the 
Old World. . „_ _ , 

On the next evening, according to promise, the Frofeeor 
wound his w»y up the steep ascent of that hill, and found 
it crowned bv a building in all respects equal to more 
widely-known Observatories of Europe. He found a library, 
enriched by the choicest collections from European store- 
houses, and on the table in the study were letters from 
distinguished observers in all parts of Europe— Herschell, 
Arago, Lord Rosse— all communicating the results of their 
observations, and soliciting contributions to Science. 

Without detaining you farther, ladies and gentlemen, 
permit me to say that that Professor has the honor to in- 
troduce that pupil, in the person of Prof. Mitchell. 

Prof. MITCHELL then rose, and, after the applause 
had subsided, spoke as follows : 

If anything could increase the embarrassment 
I would naturally feel in appearing before an aud- 
ience in this City, it is the manner in which I have 
now been presented to you. A whole tide of rem- 
iniscence has been sweeping through my mind.— 



I have been carried back to a period twenty years 
ago : How varied and wonderful has been my for- 
tune within that time ! I hope, therefore, that you 
will pardon, in the ouiset of the effort I am about 
to make to-night, any imperfections which you 
cannot fail to notice. 

I come before you, to-night, without the opportu- 
nity of choosing my topic. I come not to awaken 
your sympathies in behalf of a suffering nation : 
I coma not accompanied with the spirit-stirring 
trump of war sounding in your ears : I come not 
to rouse you to great commercial efforts, where the 
wealth of the world is to be the result of enter- 
prise. Far away from Earth, in the boundless 
Ocean of Space, mighty worlds wing their rapid 
flight, voiceless in their movement — silent in their 
career. Yet as they sweep onward in their courses, 
they are measuring out the vast periods of Time, 
and in their configurations tolling the deep-toned 
bell of Eternity itself. These are the objects to 
which I would raise your thoughts, and to which I 
would direct your attention this evening. Let us, 
then, leave this world of ours for one short hour — 
its cares, its turmoils, its woes, its confusions, and 
converse with the far-off stars. 

When we look upon the heavens — when we 
watch the movements of those silent orbs — when 
we wing our flight upward, and take in the im- 
mense range by which we are surrounded, even 
extending beyond the narrow limits of human 
vision — can we contemplate the scene without be- 
ing filled with wonder and astonishment ? This 
scene opened upon the first human eye that was per- 
mitted to see the light : and from that hour, down 
through long succeeding ages, this glorious ocean 
above us has ever fastened the attention and di- 
rected the gaze of the best and most wonderful 
minds that have adorned our Earth. The Science 
to which I would direct your attention is one which 
has furnished the theme for the investigation of the 
most exalted intellects in every age ; and from the 
earliest observations down to the present moment, 
we find the human mind occupied in its effort to- 
solve these mysteries, — grasping the most difficult 
problems, and sternly pushing its investigations 
onward and onward, until darkness disappears, 
and light — even a flood of light — breaks in from 
the heavens upon the victorious soul. And thus it 
must ever be. G-od has given these works for our 
examination, and has given to us intellect by which 
we are enabled to comprehend their structure ; 
and it is by this that we are enabled to rise — to 
climb — to ascend — to soar, by our own efforts and 
by His aid, till we stand upon the lofty summit 



4 



Prof. Mitchell's Lectures. 



of the hill of knowledge, whence we look out upon 
the wonders by which we are surrounded, and 
behold the evidences of His wisdom, power and 
glory, who hath created all things in beauty and 
in perfection. 

In the few moments that I shall detain you to- 
mght, allow me to direct your attention to the scale 
upon which the Universe is built, and to the grand 
problem involved in solving the mysteries by which 
it is surrounded. 

First, let me inquire if there be laws governing 
the movements of all these bodies, and if it is pos- 
sible to ascertain tbe nature of these laws ? Are 
they to be comprehended by the human mind ? or 
are they beyond the reach of the intellect which 
has been given us? I answer, they are not: — 
they are within our reach, and we are permitted to 
understand tbem; and in understanding tb em we 
are permitted to extend onward and onward in our 
career of examination and discovery. 

The first law to which I direct your attention is 
the Law of Motion. If a body be located in Space, 
and receive a single impulse, it will move on for- 
ever in a right line, and always maintain its on- 
ward career, never turning to the right nor left, 
and never relaxing its speed. Now, is this a ne- 
cessary law of Matter ? I answer, it is. There is 
no necessity why this law, in preference to any 
other, should have been adopted. It is the wisdom 
of God which has assigned this law to motion. 
But why should not this motion be retarded and re- 
lax and decline, and gradually die away ? Such 
laws govern other motions, and why not in this 
case ? — Again, we have the Law of Gravity ; and 
what is this ? It is a law which telis us that every 
particle of matter in the Universe attracts every 
other particle with a force which varies in propor- 
tion to the mass, and decreases in a certain ratio 
with the distance. This is a second law. — Another 
law is this: Every revolving body, in sweeping 
about from its center, has a tendency to fly from 
that center with a certain force called Centrifugal 
Force. Now, combining these three together, we 
have all the laws which govern the movements and 
guide the motions of the heavenly bodies. These 
are simple and easily understood. 

Then, with these laws at our command, let us 
examine the structure of our own System — for this 
shall be our type and model — and, passing on, let 
us essay to reach, if possible, the limits of the Uni- 
verse. Now, then, to view our System, let us 
move to the Sun and locate ourselves on that im- 
mense orb. What do we find? A vast globe, 
880,000 miles in diameter. Here we fix our point 
of observation. At the distance of 95,000,000 miles, 
as far as the eye can reach, there is a ball reflecting 
back the light thrown upon it from its great center. 
That ball receives an impulse under the action of 
that force by which it would move forever in a 
right line, but the attractive power of the Sun seizes 
it, and lo ! a planet, bathed in the light of its con- 
trolling luminary, is sweeping in its orbit, onward 
and onward in its swift career, until it comes back 
to the point whence it started. Has its velocity 
been diminished? has it lost any of its motion ? — 
No. With the same velocity with which it set out 
it reaches its starting point and onward moves 
again. 

Now, suppose we were, if it were possible, to fix 
golden rings in the path of this moving body, of 
such diameter that it might pass through with not 
<a solitary hair's- breadth to spare. Such is the beau- 
ty and perfection of its motion that from century to 
century, and from age to age, this solitary planet 
would swing in its orbit around the Sun, passing 
uniformly and invariably through these golden rings 
■with no shadow of variation from its first motion. 



But stay : While this planet is revolving in the dis- 
tance, we find another small globe, with dim and 
diminished light, commencing its movement, subor- 
dinate and controlled by the movement of its cen- 
tral body — the placet. There is a satellite — the 
Moon — added to the Earth, the two sweeping 
onward, but, alas ! the accuracy of the original mo- 
tion of the planet is destroyed forever. It no long- 
er sweeps through these golden rings. As the 
Moon passes in between it and the Sun, it adds its 
force of attraction to that of the Bun, and the 
Earth is drawn inward, no longer passing through 
the points it once so unerringly visited. As the 
Moon swings round on the opposite side, it draws 
the Earth farther from its orbit; and thus we find 
oscillations backward and forward — perturbations 
and disturbances — which it would seem no human 
intellect can grasp or unravel. 

But this bas been done. Go back 3,000 years — 
stand upon that mighty watch-tower, the Temple 
of Belus in old Babylon — and look out. The Sun 
is sinking in eclipse, and great is the dismay of the 
terror stricken inhabitants. We have the fact and 
the circumstances recorded. But how can we prove 
that the record is correct? The Astronomer un- 
ravels the devious movements of the Sun, the 
Earth and the Moon, through the whole period of 
3,000 years — with the power of intellect he goes 
backward through the cycles of thirty long centu- 
ries, and announces that at such an hour on such 
a day — as the Chaldean has written — that eclipse 
did take place. 

Such is tbe character of the knowledge we have 
attained with reference to the movements of these 
bodies. But we must go still farther. 1 announced 
to you that the Law of Gravitation declares that 
every particle of matter in the Universe attracts 
every other particle. Now then, add to the Sys- 
tem we have imagined, two interior primary plan- 
ets, Mercury and Venus — the planet Mars on the 
outside — and the seven asteroids now revolving 
between the planets Mars and Jupiter: add to 
these Jupiter with bis four moons, Saturn with his 
mighty orb of79,000 miles diameter — add his moons 
and rings also : go still farther till you reach Ura- 
nus — add h^s moons: step out still farther to the 
utmost boundaries now known of our Solar system, 
and bring in that wonderful, mysterious body, 
known as the planet Neptune, whose history is as 
yet mora wonderful aod strange than any other be- 
longing to our System : add all these together — let 
each one of these bodies act upon every other; and 
then, is it possible for the human mind to grasp 
the laws wbich hold all these bodies in their orbits? 
Can it roll back the tide of time, and tell you that, 
a thousand years ago, such and such were the con- 
figurations of all these planets and satellites? and 
not only that, but draw aside the veil from the fu- 
ture and show a thousand years hence, that such 
and such Bhall be their configurations? With all 
their disturbing influences, can such truth be elimi- 
nated, and the whole rendered clear, perfect, har- 
monious and beautiful? Yes; even this has been 
accomplished. 

But we have not exhausted the Problem of our 
System even yet : we have only taken into account 
the planets and satellites belonging to our own 
system. There are other mysterious bodies, which 
seem not to obey the laws that govern these move- 
ments. While the planets are circular in their or- 
bits and the satellites nearly the same, we find 
dim, mysterious bodies, wandering through the ut- 
termost regions of Space, — we see them coming 
closer and closer, and as they approach on* system, 
they fling out their mighty banners, wing their 
lightning flight around the Sun and speed away to 
the remotest limits of vacuity. These eccentric 






Astronomy. 



bodies— these comets— belong to our Solar System, 
and form a part and parcel of the whole : and each 
and all of these must he taken into account in 
resolving the n.ighty Problem of the Universe. Nor 
are they to be counted by tens, or hundreds, or 
thousands: their number is not less than millions. 
Neither do they revolve in the same plane on which 
the planets roll, nor in the same direction. While 
all U>e planets sweep around the great center reg- 
ularly and harmonious Jy, we find the comets pour- 
ing in from every possible point, forming every pos 
Bible angle, and passing out in every possible 
direction. And yet the perturbations occasioned 
by these bodies in their long journeys of thousands 
of years have to be made out. At this very time, 
the whole astronomical world is intently interest- 
ed in watching the return of one of these wonder- 
ful bodies. Two hundred and ninety years ago it 
visited our System for a short space. The^ two 
hundred and ninety years — its computed period — 
are now nearly expired, and at this time every tel- 
escope on oar globe is directed with the utmost in- 
tensity of anxiety to that particular region in Space 
where it is believed the stranger will first make 
his appearance. Think, that we should be able to 
trace the invisible, unknown movements of these al- 
most spiritual bodies, and be able to announce their 
return with a degree of accuracy that astonishes 
every intellect ! And yet this is the fact. 

But to what distances do these bodies penetrate 
into Space? When we remember that the peri- 
odic time of the most distant of our planets (Nep- 
tune, 2 700,000,000 miles from the Sun) is but 167 
years, and that the period of some of these comets 
is not short of three or four thousand years, how 
immense must be the distance to which they re- 
cede from our Sun ! 

Now, retaining in your minds the fact I have 
stated — that every particle of matter attracts every 
other particle — and that if these comets, in sweep- 
ing out to this immense distance, fall under the in- 
fluence of other suns, they are gone from us, never 
to revisit our System again: is it possible, then, 
that there are other systems which do not inter- 
fere with ours and with each other? Is it possible 
that these forever- wandering bodies do not come 
under the influence of other suns ? Is Space so 
boundless — is the Universe so limited — that there 
is room for more than one of these mighty systems ? 
To this point I would ask your attention. You see 
thus a partial development of the scale upon which 
the Solar System was created, and you can begin 
to appreciate the nature of the Problem of the Uni- 
verse which has been so far solved, that man might 
attain a knowledge of the System with which he 
is, in his physical nature, so intimately associated. 

But there are other objects than planets and 
comets filling the heavens. Look out upon the 
millions of stars in beautiful constellations. Be- 
hold these magnificent groups in every point of the 
heavens. Trace out that mysterious and curiously- 
wrought band, stretching from one verge of the sky 
to the other — the Milky Way. Give aid to the 
delighted eye, and through the space annihilating 
telescope see millions and millions of suns flash- 
ing upon the dazzled sight at once. Surely these 
bodies are clustered near together? They are not 
separated from each other by the same amount of 
space as we appear to be separated from them? 

Let us examine this for a moment: [The As 
tronomer, in order to find his distance from any 
heavenly bedy, ascertains precisely the point in 
the heavens where that body is located. For in- 
stance: Should we desire to-night to ascertain the 
distance of the Moon from the Earth, we should lo- 
cate one Astronomer at a given point on the Earth 
with his telescope directed to the Moon : another 



Astronomer we station at a place far distant from 
the first, with his line of sight also on the Moon at 
the same instant of time. The angle of the visual 
ray with a perpendicular to the Earth's center is 
carefully noted by each observer ; and when this 
angle is found (the base of their triangle being theiir 
distance apart) it is easy to tell at what distance 
from the Earth the protracted sides would meet — • 
— and that point of junction will be the center of 
the Moon.*] v 

Now let us try the same with regard to the Fixed 
Stars, and see whether any results are ascertained, 
We locate two observers, 8,000 miles apart, (on© 
on each side of the Earth); an»3 from these two 
points they direct their visual rays to yonder dis- 
tant orb : but alas ! the lines are absolutely paral- 
lel. The Astronomer is foiled — he pains no point 
whose distance be can estimate. What now is to 
be done ? He makes the Earth itself a grand trav- 
eling observatory, and at the extremity of the di- 
ameter of the Earth's orbit, at the end of six long 
months, when the E arth shall have swung itself half- 
way round the Sun, atthe immense distance of 200,- 
000,000 miles he again sends up his visual ray. And 
now he has a base of 200,000,000 miles — surely the 
angle at the vertex of this immense triangle will 
reveal the distance ? But, alas ! again it is almost 
insensible ; and if it be sensible at all, it cannot be 
so great as to bring the nearest of the stars nearer 
than sixty billions (60,000,000,000,000) of miles ! — 
With this immense space intervening, is there dan- 
ger that the comets shall rush against our neigh- 
boring suns, even in their long journeys of thousands 
of years? I think not. — And this is another illus- 
tration of the immense scale upon which the Uni- 
verse is built. 

Now, having reached outward to the nearest of 
these objects, let us stand and contemplate th© 
scene by which we are surrounded. Yonder 
shines Orion, with his broad and beautiful beltj, 
and yonder is the Northern Bear. These groups— 
so familiar to us — are always delightful to the eye, 
Gro with me until we reach that beautiful star in the 
northern heavens — Lyra. From that point look 
out, and what do you behold? Is there any 
change? Surely there is a new heavens? No2 
Yonder is old Orion's belt, gleaming with the same 
beautiful stars and arranged in precisely the same 
order as when we left our native Earth. All the 
change is no more than would be made by a change 
of position with your neighbor upon your owa 
planet. 

But is there no limit — no end? I answer: Thisj 
subject I propose to discuss hereafter more fully. 
I mean to take you out to-night to show you what 
there is to examine when we have reached th© 
nearest Fixed Star. And having gained this unit 
of measure, we are enabled to go on to the next, 
till finally in one unbroken succession we find them 
extending outward, and outward, and outward, till 
a long-extended series reaches in some directions 
even to 500 successive objects. Then sweep round, 
with this immense line as a radius. All the vast 
limits in the entire circuit of its range are filled 
with suns and systems that burn, and roll, and shine 
as do our own. 

Having gone thus far, it would seem that we are 
on the uttermost limits of Space ; and that the hu- 
man mind, after attaining: to that point, must there 
rest its weary wings. Not so. We are barely at 
the outskirts of one little island of the Universe — & 
small compass, condensed and united so that if we 
were even in the extreme limits which we can 
reach with our aided vision, we should grasp the 



* The words inclosed in brackets are not the language 
of Prof. Mitchell ; the Reporter having failed to catch this 
part of the illustration. 



e 



Prof. Mitchell's Lectures. 



whole — all its suns and systems, as it were, in our 
very hand itself. When we have reached these 
outer limits, and applied the powers of the tele- 
scope, exploring Space beyond, we find objects 
coming up from the deep distance and bursting up- 
on the sight, which fill the mind with wonder and 
astonishment. 

I have gazed upon these objectsin the dead hour of 
the night, when Earth's thousands of beating, throb- 
bing hearts were quieted in slumber — when the 
rapid, farions puke of business was stilled in the 
arms of sleep : from the summit of that hill, which 
my friend has described, with that mighty instru- 
ment have I swept the regions of Space. There 
was a time when my own mind could not take in 
these objects: it seemed impossible: I could not 
stretch my i imagination to their utmost limits. — 
But now put your eye to this instrument, and tell 
me what breaks in upon your vision ? Ah ! I see 
a most beautiful sight — millions of diamond points 
sprinkling the blue vault of the heavens. How 
strange is that o^her object ! Shall I tell you what 
object it is ? Go with me through the regions of 
Space — onward — onward. I see it expanding, in- 
creasing — I see diamond points in it lighting up 
with briliiancy and splendor. As we near the ob- 
ject, we find it expanding till it fills the whole visi- 
ble Universe itself; for it is nothing less than a 
Universe of Stars. Where are we now ? Look 
backward, and what is behind 1 Is our own Sun 
visible in the mighty galaxy ? Yes. I see nothing 
but a dim stain — a nebulous haze. Yet that is the 
mighty System we have left behind. This is but 
one, and it is the nearest of all of them. The great 
cluster in the constellation recalls a picture which 
I hope to present, as seen through our own tele- 
scope. Go off in another direction and you will 
bring up not only tens and hundreds, but thousands 
of these bright and beautiful star-islands of the Uni. 
verse, strewed throughout the vast regions of Space. 

It is the business of the Astronomer to study not 
only his own System, but to contemplate the mil- 
lions of stars, and to go still farther out to those 
mysterious nebulous objects with which the heav- 
ens are filled, and tell if, in the long lapse of ages, 
some mighty change may not be working in these 
curious and wonderful objects. — But I have already 
nearly exhausted the allotted time. 

— I cannot separate from this audience to-night 
without referring to the present condition of the 
Observatory now under my charge. I do this part- 
ly by way of apology, and partly for the purpose of 
giving you to understand the reason why I am 
now before you. Those of you who heard me last 
year, will remember that after having devoted five 
years of continuous effort to the accomplishment of 



this great enterprise — after having visited Europe 
and returned again, I had succeeded so far as to se- 
cure a site, to erect the principal building, and to 
place upon its base one of the noblest telescopes 
that has ever been directed to the examination of 
the heavens. Two years ago I found myself in- 
volved in a debt of nearly $5,000. This was incur- 
red unwillingly on my part, and by stern necessity 
was I driven into the embarrassing position. It hap- 
pened that the individual from whom I received 
the title-bond, had entered an addition, that unless 
the Observatory was finished by the 8th of June, 
1845, the whole should revert to himself again. It 
was to save this that I found it necessary to assume 
the debt, amounting to the sum mentioned. When 
I had gone thus far. it seemed that all my difficul- 
ties were at an end ; but it was not so. When the 
Observatory was thrown open to those only who 
had paid the stock — when it was found tb»t the 
multitude were not to assume to themselves the 
management of its instruments, there arose a pre- 
judice that no strength of resistance could stem. — 
My friends found it necessary to leave me alone in 
this position. It was impossible to move any kind 
of influence or to bring anything to bear which 
could assist me in this peculiar position. Under 
these circumstances I ventured to leave my home, 
and I first made a public effort in Boston. Fortu- 
nately, I was there received with open arms; and 
such were the nature of the attentions I met, that 
on my return home, the reflex influence was strong 
enough to bring back my old friends who had for a 
single moment hesitated, and the $5,000 were at 
once advanced. 

But we were not yet through : our building was 
not furnished ; the remaining instrument had to be 
obtained ; no less than three or four thousand dol- 
lars more were to be raised to complete the enter- 
prise. I was obliged to make a second effort ; and 
many of you remember with what fear and trepid- 
ation I ventured before you a year ago. Nothing 
but stern necessity could have driven me to occu- 
py the position I then occupied. I ventured upon 
your kindness, and in venturing I was not disap- 
pointed ; for such was the kind response I met both 
in this and your sister city, Brooklyn, that on my 
return home my friends got around me once again 
and said to me, " Make out your estimate and the 
money shall be raised forthwith." (Applause.) 

Ana now I have the pleasure of announcing to 
you, that at the end of five and a half years of per- 
petual toil and unrelaxed effort, in that wilderness 
city there stands, finished and paid for, one of the 
most magnificent observatories that graces the sur- 
face of our globe. (Applause.) 



LECTURE II. 



History of the Developments of Astronomical Science with reference to the Moon.... The Waxing acd Waning of the 

Moon— Its Change of Position in the Heavens The Second Grand Discovery of the Movement of the Sun First 

Discovery of a Planet— Discoverer unknown First Exhibition of a Solar Eclipse Explanation of the Causes 

of an Eclipse of the Sun. and Method of Calculating its Return The Individual who first Predicted an Eclipse 

unknown.... Causes of the Eclipse of the Moon. .. .The Figure of the Earth revealed to the Early Astronomers 

Influence of the Moon on Civilization, &c The old Greek Theory of the Solar System Tne Copermcan 

Theorv The First Difficulty, according to this Theory, of Locating the Moon— Its Solution Keplers Discovery 

of the"" Laws of Planetary Motion. ...Newton's Discovery of the Law of Attraction— Manner of Determining 
that Law— Difficulties Newton had to Encounter from Want of True Data— Discovery of the Source of hi3 
Error and Influence of his Discovery upon his Mind. 

Ladies and Gentlemen: It has been my for- I eight of those occasions I have been greeted by ex- 
tune to appear before a public assembly in this actly such inclement weather as we have to-night. 
City eleven times in the course of my life, and on | There seems to be some fatality attending my 



Astronomy. 



coming here, and I fear, if it goes on much longer, 
yon will come to the conclusion that I had better 
always stay at home. 

— I have before stated the fact that the Science of 
Astronomy has furnished to the human intellect the 
widest and noblest field for its efforts. As my 
Course of Lectures will be necessarily short, 1 
shall embrace the whole range of the Science and 
accomplish as much in this Course as is possible. — 
I propose, therefore, to direct your attention to spe- 
cific objects. Follow me then to-night, if you 
please, through the History of the Developments of 
Discoveries made with reference to our nearest 
neighbor — the Moon, 

The early history of Science we know is lost. — 
We may trace back the record of its movements 
until we see that there was a Science of Astronomy 
anterior to the earliest date which History can 
reach. We may then take up Tradition — stepping 
still farther back — and there again we stop and 
ponder upon the fact that there was a Science of 
Astronomy anterior even to Tradition. Thus we 
are lost in the obscurity of past time, and, having 
nothing more to guide us upon which we can rely, 
we must resort to Speculation. But let it be re- 
membered that this speculation is of such a charac- 
ter that it is absolute certainty, and, if it be proper- 
ly conducted, it will lead us to results entirely relia- 
ble. I shall be obliged, then, to begin with Specu- 
lation. 

In turning the eye to the heavens, the strong 
probability is that the veiy first astronomical obser- 
vations made upon any moving body were those 
made upon the Moon. This attracted the wondering 
gaze of every eye, — its curious and extraordinary 
changes, and the rapidity of its movements, were 
so different from those of any other heavenly body. 
While the Sun was ever bright and round — while 
the other planets always shone with a serene and 
steady light — while the fixed stars shed forth the 
same unvarying degree of splendor year after year, 
it was found that the Moon was constantly chang- 
ing. On one evening it was observed to be the 
slender silver crescent, close beside the Sun: it 
was watched from night to night, receding from a 
line with the Sun, and increasing in brilliancy, 
till, finally, it was found to rise in the East in full 
orb while the Sun was sinking in the "West. Then, 
as the nights rolled on, the light was discovered to 
decrease, until, when it again came round in con- 
junction with the Sun, it had entirely disappeared. 
These changes were doubtlessly the first observed. 

But there was another point which early attract- 
ed the attention of man. When the grouping of 
the stars in the heavens had first been made — when 
it was seen that they held invariable relative posi- 
tions to each other, the next point was to watch 
and see if the Moon held its place among the stars. 
Here arose a most wonderful discovery. The 
Moon did not hold its place among them. What 
did it do 1 It was found, in the next place, to be 
moving contrary to the motion of all the heavenly 
bodies, which appeared to make regular diurnal ro- 
tations. The Moon was heaving upward, while at 
the same time it had a general diurnal motion. — 
Here was the first discovery ever made with re- 
gard to the Movements of the Heavenly Bodies. 

For a long time it must have been a matter of 
perplexity whether this motion of the Moon was 
real, or was occasioned by the fact that the whole 
sidereal heavens were sweeping past the Moon. — 
How was it possible to determine this question ? 
If they had only this object to examine and no 
other moving bodies were found, then would it have 
been impossible to have settled the question 
whether this motion actually belonged to this ob- 



ject alone, or whether the whole Sphere of Stars 
wheeled round more ramdly than the Moon. 

But after a little while they found that the Sun 
in like manner partook of a similar motion. They 
watched the setting Sun. How many of us have 
done the same thing, for the like purpose 1 ' They 
saw certain bright stars first making their appear- 
ance, apparently near the Sun, as it sunk to rest. 
Night after night they watched, and found to their 
astonishment that these broad groups of stars were 
coming downward to meet the Sun, and at every 
successive day they were nearer and nearer that 
luminary. The Sun is heaving upward, said they, 
to meet the stars, as they are sinking down under 
the horizon ; and inasmuch as this phenomenon did 
not differ from that of the Moon, it settled the ques- 
tion, at once and forever, that this motion of the 
Moon and the Sun was really in no sense belonging 
to the heavenly bodies among which they appeared 
to be located. Here, then, was a second grand dis- 
covery — the Movement of the Sun. 

But as they continued these examinations they 
had occasion to refer the Sun to a very brilliant, 
beautiful star, that was found to be visible to them 
after the Sun's setting. This was regarded as a 
fixed star among the rest ; but, by continuous ex- 
amination, it was found this star was moving down- 
ward to meet the Sun. It did not hold its place 
among the rest. What could be the meaning of 
this ? He who first fixed his eye comprehendingly 
upon this object, how intense must have been his 
emotions ! What is this, hitherto ^regarded as a 
fixed star ? He watches it till finally it is lost in 
the splendor of the Sun. What now ? It has been 
found that all the bright stars among which the Sun 
appears, move upward in the East in the morning 
just before the Sun rises. Might it not be that this 
star will pass by the Sun and make its appearance 
in like manner? We can imagine this individual, 
morning after morning, with his gaze fixed on the 
eastern sky, watching the reappearance of his lost 
star. At length it is found : there it is, on the other 
side of the Sun! 

Here, then, is the first discovery ever made of a 
planet by the human eye. Who discovered it 1 — 
Alas ! his name — his country, is forever lost. But 
we know this to have been the process. Having 
found one of these moving bodies, it was not difficult 
to find others. But it is unnecessary to go into an 
explanation of the manner in which other planets 
were discovered, and I will revert to the Moon. 
Up to this time no explanations of the changes of 
the Moon were divined — it was impossible to divine 
them. 

Another phenomenon, more wonderful, more ter- 
rific than all, now came to impress itself upon the 
mind and awake its energies : it was the exhibi- 
tion of a Solar Eclipse. No eye, even at this day, 
has ever gazed upon this startling scene without 
experiencing a sense of awe or fear. The idea 
that the great Source of Light is waning — is dying — ■ 
is passing away from the heavens, always chills the 
blood and fills the mind with terror. What, then, 
must have been the effect produced upon the minds 
of the early inhabitants of' the Earth by this phe- 
nomenon — while the causes which produced it 
were unknown, and it was impossible to predict its 
coming — when, at the noon of a gorgeous and sunny 
day, it presented itself to their astonished gaze 1 
Surely, we may imagine that, after such a startling 
phenomenon, the most powerful intellects were con- 
secrated to the investigation of this mystery. 

Now, I shall venture to attempt; an explanation 
to go far enough to show to you how it was that 
the first eclipse was predicted, so that you your- 
selves can, with the eye alone, make the requisite 
observations and attain sufficient knowledge to be 



c 



Prof. Mitchell 1 s Lectures. 



able yourselves to predict the coming of such an 
event. This may seem veiy difficult — and it is mar- 
velous, even now, with all the aid of astronomical 
tables, and all the knowledge we have derived from 
the storied Past. How it could have been done 
thousands of years ago, when the true knowledge 
of our System did not exist, is most remarkable and 
entirely inexplicable. Let us examine into this 
matter. 

In the first place, the attentive eye marked the 
fact that when an eclipse of the Sun occurred, no 
Moon was visible. This was a very important 
point; and, aroused by the discovery of this fact, they 
watched the movements of the Moon and marked 
its position before the coming eclipse. The next 
night after the eclipse they found the Moon close to 
the Sun — a silver crescent, actually located in such 
a manner that if it pursued its wonted orbit it must 
have passed very near the Sun at the very time the 
eclipse took place. The Moon was last seen on this 
side — immediately after the obscuration it occupied 
the other side. They joined these two points, and 
by the rate of motion of the Moon calculated how 
long it took for the Moon to come up to a junction 
with the Sun, and it was found to be just such 
as to allow the Moon to come in conjunction 
with the Sun at the very time of the eclipse. Hence 
they reached the conclusion that the Moon was 
passing between the eye of the observer and the 
Sun, and in that manner the light of the Sun had 
been intercepted. Here was an explanation of 
the extraordinary phenomenon of a Solar Eclipse. 

Bat how was it possible for them to calculate the 
return of an eclipse ? This will require more at- 
tention. I beg you to remember that we have no 
history going hack sufficiently far to record this 
wonderful discovery — even tradition knows nothing 
of it. We must then go back in imagination, and 
speculate concerning it. 

First, then, it was remarked that the track 
pursued by the Sun and the Moon among the 
fixed stars was circular. Now if it were possible 
for me to mark out the track of the Sun in the 
heavens — if it would, for our accommodation, leave 
a broad belt equal in breadth to its diameter — if the 
Moon in like manner should leave the mark of its 
track, these two bolts would not coincide, but 
would cross each other in two opposite points — 
These are what are called the Nodes. You will 
understand what follows without difficulty. Now, 
in order that it should be possible that the eclipse 
should take place, you will readily perceive that 
it was necessary, not only that the Moon should be 
in conjunction with the Sun, but it mast actually 
cross the track of the Sun when in conjunction, in 
order to make an eclipse. The Moon must be in 
one of these nodes or an eclipse cannot take place. 

But again, it has been already observed that an 
eclipse cannot occur except at New Moon. Com- 
bine these two facts. If it should so happen that 
the New Moon should come in just at the instant it 
was crossing under the disc of the Sun, then won ! d 
the Moon interpose itself between the eye and the 
Sun and an eclipse would necessarily occur. 

Now then, to find out that period : Let us go, in 
imagination if you please, to the top of some moun- 
tain peak, where the first Astronomer — immured 
from the world — carries on his nightly observa- 
tions. He has reached to the knowledge of the 
fact that there will be an eclipse of the Son if the 
New Moon occur at the time she is in her node. 
He already knows the time for the New Moon to 
come in, which is fixed and certain. He believes 
he can compute the time when the next node will 
come round, and to do it he seizes the aid of the 
Moon to-night. He runs onward till he finds when 
the New Moon will appear, and discovers that 



when it comes round it is not in the act of crossing 
the Sun's path. He runs round another cycle and 
finds again that it is not on the Sun's track. He 
extends his investigations still farther from one lu- 
nation to anorhei*, — he finds the New Moon ap- 
proaching nearer and nearer to the desired place, 
till finaily it comes exactly to this point. Thecom- 
pution is marked. " There," he says, " when that 
day arrives, I announce to the inhabitants of the 
world that the Sun shall lose its light." 

With what anxiety be must have watched the 
coming of that day ! How slowly did the revolv- 
ing Moons pass by ! At last the day arrives ; — he 
retires to his rocky summit, there to awaic the test 
of his triumph or his defeat. The Sun rises, bright 
and beautiful — it mounts the heavens, and scatters 
glory in its path. While the mortal world below 
are engaged in the avocations of business and the 
pursuits of pleasure, he is watching with intense 
anxiety to know what the result will be. But in 
the very noon of the day his triumph arrives. The 
Sun begins to fade — it wanes — it dies ! The terror- 
stricken millions below cry with agony ; while this 
lone man, on his bleak and barren watch-tower, with 
out stretched arms offers his thanks to the God of 
the Universe who has crowned his efforts with suc- 
cess! (Applause.) 

But, alas, for human fame ! Surely that individ- 
ual might have hoped to believe that he who had 
first predicted the coming of an eclipse, who had 
removed the causes of terror which this phenome- 
non had spread among the inhabitants of Earth, 
should have his name engraved upon the tablet of 
Fame " with a pen of iron and the point of a dia- 
mond." Yet his name — his nation, is lost forever ! 
No history reaches so far back — no tradition can ex- 
tend to the point of time when he lived, or where. 

Now, by a most remarkable and wonderful ar- 
rangement of the lunations, on the return of the 
New Moon it is found that, after we have predicted! 
one eclipse, if we will go on and record each succes- 
sive eclipse for the period of between 18 and 19 
years, at the end of the cycle of 223 years they 
will have run round what might be called an orbit, 
and again occur on the same days. Hence, after 
they had recorded eclipses for one such cycle, there 
was no difficulty in predicting an eclipse at any fu- 
ture time. The coincidence, however, is not exact. 
For, if an eclipse occured on the 19th of March, 
3.000 years ago, the succession of the cycle may in 
the course of time wear gradually around and dis- 
appear ; but many years must roll away before, on 
the recurrence of the cycle, an eclipse will not 
take place. 

As soon as it was possible to understand the 
cause of the eclipse of the Sun, the human mind was 
directed to the investigation of the cause producing 
an eclipse of the Moon. This was far more diffi- 
cult, and for this reason : — In the eclipse of the Sun 
they had watched the coming up of the Moon to 
the Sun, its passage across the Sun's disc, believ- 
ing without question that the eclipse was caused 
by its interposition between them and the Sun, and 
that it occurred only at New Moon But what was to 
interpose itself between the beholder and the Full 
Moon ? There seemed to be nothing in the heavens. 
Upon reflection, the human mind bethought itself 
that every body which revolves in the light of an- 
other luminous body, will cast a snadow beyond in 
a right line with the light itself. Now if the Earth 
is opaque, it might intercept the light thrown upon 
it from the Sun, casting a shadow toward the hori- 
son, and might it not be projected far enough to 
reach the Moon itself, so that the Moon in passing 
into the shadow, having no light of its own, would 
be obscured 1 Here is an explanation of the cause 
of the Lunar Eclipse, revealing to the early As- 



Astronomy. 



tronomers the fact that the Moon was not self-lu- 
minious. 

The explanation of the Phases of the Moon 
is easy. If it be a globe, or sphere, and only bril- 
liant in consequence of the reflection of the light 
from the San, it became necessary that the illumi- 
nation shuuld always be at the time when ihe 
Moon and the San were in contrary positions rela- 
tive to the Earth. When the Sun was setting and 
the Moon was comparatively near to the Sun, and, 
of course, between the observer and the Sun, it 
was impossible to see the whole illuminated sur- 
face of the Moon, and indeed sometimes almost 
none at ad. Bat as the Moon gradually receded 
from the Sun, night afcer night, after a time it came 
to occupy an easterly position, when the light of the 
San falling upon its surface was thrown back at a 
very acute angle upon the eye of the observer, and 
the Full Moon was presented. These changes 
were going on from lunation to lunation, and, once 
observed, were easily comprehended. 

While the Moon thus revealed to them the causes 
of the eclipse of the San, and the reason of its own 
phases, it also revealed to the early astronomers 
the figure of oar Earth. How did this occur? It 
was found, when the Moon passed into the shadow 
of the Earth, that the line cat out on the disc of the 
Moon by the shadow was an arc of a circle, and as 
it passed farther and farther on. even to the entire 
obscuration of the Moon, it still appeared in a 
form nearer a complete circle. Now it was im- 
possible that any other than a globularfigure should 
cast such a shadow upon the surface of the Moon. 
The Moon, then, first revealed the figure of the 
Earth upon which-we live ; and, strange to tell, that 
same Moon, in our own day, has given us a more 
perfect knowledge of the figure of the Earth than 
can be derived from any measurements with the 
most accurate instruments we yet possess — This 
matter I shall undertake to explain hereafter. 

We find, on running back to past history, that 
observations were made upon the Moon, at Baby- 
lon, 2,250 years before the Christian Era. And 
these observations, upon the taking of that city by 
Alexander, were said to have been presented to 
Aristotle. The truth of this we cannot know ; but 
one thing we do know — that on the 19th of March, 
2,567 years ago, there was an eclipse of the Sun 
observed and recorded in the tower erected in that 
mighty city: on the 8th of March in the following 
year there was another ; and on the 4th of Septem- 
ber in the next year there was another. And we 
know and understand the peculiarities belonging 
to these antique observations. 

These are, perhaps, among the earliest observa- 
tions — and of such importance are they in linking 
the Past with the Present, that but for them wa 
would at this time be comparatively ignorant of the 
movements of that wondrous orb which does more 
for toe civilization of the world than any other one 
thing of which we have a knowledge. I pronounce 
this to be true without hesitation. If it were pos- 
sible, now, to trace with perfect precision the exact 
position of the Moon, we should accomplish more 
for Commerce, for Science, for Civilization than could 
be done in any other way. Why? Because then 
the tempest-tossed mariner upon any ocean — over 
whom days and weeks had passed without his see- 
ing the San or stars— the moment this silver orb 
made its appearance again in the heavens, would 
be able with perfect confidence to exclaim: "I 
know exactly in what part of the globe I am situa- 
ted ; the smallest observation gives me my latitude, 
and the position of the Moon my longitude." Hence, 
I say, it is of the utmost consequence that we should 
have these old observations ; for by linking them 
with those now making, we are able to approxi- I 



mate to the accomplishment of this grand design 
more fully. 

But as we come down through the tide of Time, 
we find a particular theory adopted with regard to 
the whole System with which we are united — the 
old Greek theory, to which I will just advert. It 
located the Earth in the center, and made the Mooa 
the nearest object, and the Sun next. Now it hap- 
pened, curiously enough, that there was one truth 
in the theory : the Moon did revolve about the 
Earth. 

When Copernicus presented his theory, and trans, 
ferred the fixed center to the Sun, causing the plan- 
ets to take proper positions, rescuing the Earth 
from its false position and sending it revolving round 
the San, the question was, What is to be done with 
the Moon 1 There seemed to be a difficulty here. 
The query was : Is the Moon a planet like the rest? 
Perhaps many of my audience have not thought of 
this. How many of us have asked the question — 
" How do we know that the Moon revolves ?" Be- 
cause the books tell us so? We are generally in 
the habit of receiving facts in that way. I do not 
remember ever to have seen an explanation of this 
in any book. But Copernicus reasoned in this way. 
Said he : I do not believe the Moon revolves in an 
orbit interior to the Earth's, because I find that 
evinces a mircle ; the Moon in that case should 
never leave the Sun but to a limited distance. Now 
the Moon does leave the Sun, and moves off till it 
is directly opposite, and then comes around again 
up to the Sun. I therefore say it does not revolve 
interior to the Earth's orbit. In the next place, it 
does not revolve exterior to the Earth's orbit ; for I 
find the motion of all the planets exterior to the 
Earth, at certain points of their career becomes 
slow — it is arrested — they stop — retrograde — they 
stop again, and then take up their onward motion. 
Now I understand why it is that we, being on the 
surface of a circular globe must have these changes 
exhibited to us. But the Moon never stops and re- 
trogrades — it is ever moving onward, and therefore 
is not exterior to the orbit of the Earth. 

Here was a farther absolute demonstration. It 
could not be either interior or exterior — therefore 
it was no planet at all. Now the phenomena ex- 
hibited by the Moon were perfectly accounted for. 
If— upon the hypothesis that you make the Earth its 
center — it revolves about the Earth, it is our 
satellite, ever accompanying us in all our move- 
ments. 

But we come down still farther in the history of 
our neighbor. When Kepler discovered the two 
laws of planetary movements — that they revolved 
in orbits not exactly circular, but a little elongated — 
elliptical as they are called ; when, in like manner, 
he had discovered, by tracing them up, that a 
line drawn from the San to any of the plan- 
ets always swept over equal areas of space 
in equal times — and when, at the end of 
seventeen long years of toil, he had also discovered 
his last great iaw, which linked all these isolated 
planets into one grand unit, making the Sun always 
the center, it seemed that nothing more remained 
to be done. Bat immediately the question arosei 
What holds these mighty globes steady ? What 
power reaches out to them and prevents them from 
breaking from their orbits and wandering away 
into the blackness of darkness ? The resolution of 
this problem was reserved for the immortal Newton. 
Kepler himself gathered some faint glimmerings of 
the great cause — that there was a power of attrac- 
tion existing in bodies, mutually operating upon 
each other ; but he did not attain to the demonstra- 
tion of this fact. This was reserved for that great 
man to whom we owe our knowledge of the laws 
of attraction. 



10 



Prof. Mitchell's Lectures. 



Here, if you will allow me, I will attempt to ex- 
plain the manner in which Newton conducted the ar- 
gument which led him to the grand result. I am con- 
fident that although there are many here who have 
given comparatively little attention to Astronomi 
cal Science, they will be able to follow me readily 
in this explanation. Newton began where Kepier 
left off. The latter announced that bodies were at- 
tracted to each other, and by a force which he be- 
lieved decreased according to a certain fixed law : 
and it was to prove this «that Newton made his in- 
vestigations. In the first place, he announced this 
as a law, according to his belief: That every body 
attracts every other body by a force which varies 
inversely as the square of the distance. If a body 
be located at a distance one. the force of its attrac- 
tion we will call one, Now remove this body as 
far again to a distance tico, and the attractive 
power will be one-fourth. — at a distance three, one- 
ninth, and at a distance four, one-sixteenth ; and 
you can carry out the law to any distance. 

Now, to prove the truth of this law was the ques- 
tion. In the first place, it is manifest that, whatever 
be the law of attraction, it wid be clearly and posi- 
tively determined by the amount of velocity it is 
capable* of impressing upon a falling body This is 
intelligible to all. If from this point I let fall any 
objectlo ward the Earth's surface, under the influ- 
ence of the force of attraction suppose itfeil sixteen 
feet in the first second of time— this sixteen feet 
will measure the force of attraction at the Earth's 
surface. If it were possible to go 4,000 miles high, 
and from that point, as remote from the surface of 
the Earth as my first station at the surface was dis- 
tant from the center, and then drop a body, meas- 
ure the space through which it falls, and find it 
to be one-fourth of sixteen feet in a second, this 
would be proof that the law was true. But sup- 
I rise still higher, 12,000 miles above the center of 
the Earth, and there find the space through which 
this body falls is a ninth part of sixteen feet in a 
second — here is another confirmation of the law. 
And if. as I increase my distance every time by the 
radius of the Earth's circumference, I find the same 
law holds true. I pronounce, without hesitation, that 
this is the Law of Attraction. 

But I cannot rise in this way, to a distance of 
twelve, eight, or four thousand miles. Yet may I 
notcarry my observations to a certain hight ? Yes ; 
but to such a comparatively small distance that the 
difference will be inappreciable. Alas, for the per- 
son who undertakes the experiment ! such is the 
minute difference, even when he has attained the 
greatest hight ever attained by man, it cannot be 
appreciated. 

What then was to be done ? No one could as- 
cend above the Earth to perform these experi- 
ments. But the mighty intellect of Newton stretch- 
ed still farther, and our old friend, the Moon, was 
brought in to play the part of this falliag body ! 
What! do you ask — Is the Moon falling toward the 
Earth, and does Newton seize it and stop it, and 
then compute with what velocity it should come 
toward its central planet ? No : This is not pos- 
sible. But. let me explain. Here is the Moon: — 
Now let us start with the Moon when it was first 
projected in its orbit. Under the action of the im- 



pulsive force it would have moved off in a straight 
line, with a certain determined velocity, which we 
can measure. If this impulse had not been piver. 
to it, and it had been left free in Space, it would 
have dropped toward the center of the Earth with 
acertainvelocity.which we can also measure. Now. 
under the action of these two forces, it does not obey 
either of them, but takes a direction intermediate 
between the two, and swings in a carve about the 
Earth. And here is the stated point: If, under 
the action of an impulsive force, it would in a sec- 
ond of time reach that point in a straight line, under 
the attraction of toe Earth it is drawn down, and 
the amount by which it is drawn down is the amount 
through which it falls during that second of time. 

One more grand point is to be accomplished, 
and we are through. First: Inasmuch as the 
Moon is falling, it is necessary to note how much 
it falls. That is easily measured : all we have to 
do is to remark the amount of declension from a 
straight line which it would have pursued in a 
second of time. A straight line is easily measured, 
and gives the value of the distance through which 
a body located at the Moon will fall toward the 
Earth in ore second. 

Now the erand point is whether that distance is 
what it ought to fall, under the hypothesis of the 
Law of Gravitation. When Newton undertook 
this investigation he was not provided with accu- 
rate data. It was easy to compute bow far a body 
should fall in a second of time — every person can 
do that. Only follow this law, beginning with 16 
feet a second at the surface of the Earth, or at the 
length of the Earth's radius. Just square the dis- 
tance, which will be successively 2, 4, 9, 16, and so 
on, till at the distance of the Moon, or 60 times the 
length of the Earth's radius, it will be 3,600. Since 
this computation was so easy, all that was neces- 
sary was to measure the space through which the 
Moon did fall, and if they were equal, then of 
coarse the demonstration was made. 

Yet, alas for the toil of the philosopher ! His 
data were incorrect, and for seventeen years did 
he goad his mind to the subject, toiling day and 
night to make this coincidence perfect, but it would 
not agree ; so he threw his laborious computations 
away in despair. , 

But, in attending a meeting of the B,oy al Society 
in London, he happened to catch the sound of the 
voice of an individual who was talking about a 
recent measurement of the circumference of the 
Earth. That was principal element entering into 
the computation. The new measurement differed 
from the old. Here, thought he. may be the source of 
my error. He takes down his old computations, and 
substitutes the new measurement of the diameter 
of our globe, which makes a difference in the pro- 
portional distance to the Moon. The result he 
anticipates is coming out. Bat his nervous sys- 
tem sinks beneath the intense excitement — he 
yielded up the computation to a friend, for be could 
not makeit himself. The coincidence was perfect — 
the grand demonstration was made — the Law of 
Gravitation was proved. At last he had grasped 
the Key to the Mysteries of the Universe, and held 
it with a giant hand. (Great applause.) 



Astronomy \ 



11 



LECTURE III. 

Adherence to Established Notions of Nature's Laws — Natural Laws the Expression of God's Will.... Difficult to 

Conceive the Object of Creation Perpetuity a Design A Simpler System Possible PerturbationsDiffi- " 

cult to* Calculate A Higher Design than Mere Stability Newton's Calculations— Orbitical Curves— Figure 

of the Earth— Centrifugal Force resulting from Rotation— Inclined Plane and Centrifugal Force Equal Other 

Orbs kept within Limits of Perpetuity Elliptical Figure of Orbs affect their Motion The Equinoctial 

Points — Egyptian Observations — Precession of Equinox — It Results from the Elliptical Figure of the Earth — Ex- 
planation of Causes of Precession Tides — Causes of Tides Variation of Orbits from Ellipse to Circle — 

Effects upon the Moon's Motion Telescopic Appearance of the Moon— Measurement of Hights and Distances 

in the Moon — Absence of Atmosphere on the Moon, &c. 



Ladies and Gentlemen: In the examination of 
the Structure of the Universe, we are very apt to 
adopt the idea that it is impossible that any other 
system than the System which we now know, 
does or could exist. We go even farther, and 
conceive the idea that the great Laws which now 
govern, are the only laws which could govern, — 
that the Law of Motion, for example, is a neces- 
sary Law of Matter, and that the Law of Gravita 
tion is a Principle inherent in Matter, which can- 
not be severed from it. These are views which 
are too generally entertained ; and in the outset of 
what I am about to say this evening, I beg to be 
understood as to my own conceptions with regard 
to these important points. 

I believe that "In the beginning, God created 
the Heavens and the Earth ; " that he selected the 
Laws by which He would govern the Universe, 
and that these Laws are the perpetual and un- 
changeable expression of His Almighty Will. But. 
do you ask the question : Could this System of 
ours, upon which we look with so deep an interest, 
have been differently arranged, and yet have ac- 
complished the grand objects which it seems de- 
signed to accomplish 1 That depends entirely 
upon what we conceive to have been the grand ob- 
ject. I contend it could not have been differently 
arranged with the objects in view which we have 
reason to believe were had at the time of its con- 
templated organization. But do we, on the way 
through our examination, conceive fully and en- 
tirely — or even approximately — the grand object 
of this scheme by which we are surrounded? I 
know it is difficult to touch this subject; it is hard 
to make myself understood : but a very few mo- 
ments of explanation, I trust, will be sufficient, — 
and then I will proceed to the application of the 
Laws of Gravitation. 

In the first place, the great design in constitu- 
ting the System by which we are surrounded and 
with which we are associated, was to give to it 
perpetuity, so that it may not have the elements 
of its own dissolution and decay within itself. 

Let us stop here for a moment and see whether 
this object could have been attained in any other 
way. I believe that it could have been attained 
in a much simpler way than it now is. Do not mis- 
understand me, for I use the expression with all 
reverence. If the Law of Gravitation had been a 
little different ; if instead of every particle of mat- 
ter attracting every other particle in the Universe, 
this law had been announced thus : The Sun shall 
attract the planets, but they shall not influence 
each other — the planets shall attract their satel- 
lites, but these revolving satellites shall haveno at- 
tractive influence upon each other — the Sun shall 
draw the comets from the depths of Space, and 
shall bring them to itself and throw them off again 
without their being influenced in any degree by 
approximation to the planets among which they 
move, — then we should have had a stable system — 
one that would have endured throughout the cease- 
less ages of Eternity itself. And how simple this 
system would have been in comparison to the one 



which now exists. In the one by which we are 
surrounded, we find perturbation upon perturba- 
tion, disturbance upon disturbance, causing re- 
action throughout the whole, till every movement 
becomes so complicated and involved that it seems 
almost impossible to understand or follow their de- 
vious operations. 

On the contrary, had the other system been 
adopted, so soon as we should have attained to the 
true position occupied by one of these beautiful 
orbs in its revolution above us — its uniform move- 
ment being fully understood — from century to cen- 
tury, from age to age, as far as the imagination can 
stretch in point of time, no change, not a solitary 
deviation, ever would have been made from the 
route which it first pursued. 

But there was a higher object to be attained in the 
Structure of the Universe, than mere stability. We 
have shown how that might have been done. But 
this complicated System was given for our instruc- 
tion, as a grand problem which would lead us in our 
investigations onward and upward to Him who 
built the Universe in Wisdom and with Power. — 
And hence we find the complication by which we 
are surrounded — and in this complication we find 
that which stimulates and excites the human intel- 
lect to its highest possible attainments. 

With this explanation, allow me to refer, for a 
single moment, to the concluding part of my last 
Lecture. I attempted to exhibit to you the process 
of reasoning by which Newton accomplished the 
demonstration of the Law of Gravitation — to show 
you how, by the examination of the movements of 
the Moon in its orbit and the amount of space 
through which it fell toward the Earth, under the 
inflaence of some attractive force there located, he 
found that force varied according to a certain law, 
to wit : The Inverse Ratio of the Square of the 
Distance. 

The next point made — after he had attained this 
first one — by which he became convinced that this 
law was true, was to extend his examinations on- 
ward to see whether, in all other instances, this 
might be applied with success, and if the move- 
ments of the other heavenly bodies could be account- 
ed for on this hypothesis. He therefore commenced 
the examination of the great problem of which this 
was to be merely a corollary. He propounded to 
himself this vast question : Suppose a body to ex- 
ist in Space, located in such a manner as in a sense 
to be isolated. Now, as this body is endued with 
this power of attraction which shall follow in the 
inverse ratio of the square of the distance : What 
would be the nature of the curve described by the 
body revolving about this center, when under the 
influence of force varying as did the force of gravity ? 

As I have already related, Kepler had found that 
the planets described elliptical orbits, having one 
axis passing through the center longer than all the 
others, and another axis perpendicular to this short- 
er than all the others. Inasmuch as they did thus 
revolve, Newton hoped and believed that when he 
should have arrived at the truth in the investigation 
of this problem as to the curve described, that 



12 



Prof. Mitchell's .Lectures. 



would prove to be an ellipse, inasmuch as they 
were known to revolve in these curves. He takes 
the analysis which he had conjured up for his aid, 
brings a!l his intellectual power to bear upon the 
problem, and subjects it to an irresistible analytical 
reasoning, of which all the data were perfectly 
within his grasp. Tie result comes out — in a kind 
of cabalistic, algebraic characters which I cannot 
explain to you at this time. But it is sufficient to 
say, that there wa3 an additional meaning; and 
the query was, What was that meaning? Was it 
an expression exhibiting the curve of the ellipse ? 
It was strange, even to Newton, what that expres 
sion was ; it did not look familiar ; it did not exhibit 
the proportions of this elliptical curve — and what 
could it be? With much labor he unraveled the 
mystery, and to his astonishment he found that, in- 
stead of being the equation of the ellipse, as it is 
called, it was the equation — the general expression 
— of no less than four curves : the circle, the ellipse, 
the parabola, and the hyperbola were all in like 
manner involved; each and every one of these 
carves being- the expression to which he arrived as 
the result of his examination. But what could be 
the meaning of all this ? He looks out upon the 
System for an answer; and lo ! a comet, coming in 
from the distance, sweeps round the Sun in a curve 
called the parabola; another describes the hyper- 
bola; the planets revolve in ellipses, and their sat- 
ellites describe circles. Here you perceive was a 
very unlooked for result, and it became evident that 
either one of these four curves might be described 
about a body revolving about a center under the in- 
fluence of the Law of Gravity. 

When this result was reached, the next inquiry 
was this : Is it true now that every particle of 
matter attracts every other particle according to 
this law ? The examination of this question pre- 
sented many difficulties. How was it to be re- 
solved ? How could he tell whether the force of 
attraction in the Earth for example, was located in 
the central point of the globe, or distributed 
throughout the whole mass, existing equally in 
every particle of that mass. He commences by 
examining the figure of the Earth — applies the 
law upon the hypothesis that every particle did 
attract every other particle — he finds the Earth 
revolving upon an axis, and perceives what is pro- 
duced by the operation of this law upon the earth. 
If, in the outset, the Earth were created perfectly 
spherical, he finds, under the influence of the swift 
rotation upon the axis, it cannot maintain that 
figure: its form must be changed and another 
given it in process of time ; and he even predicted 
before the meastirement had been made, what it 
must be, and determined what should be the ratio 
of the polar and the equatorial diameters of the 
Earth. 

But if the figure of the sphere were changed from 
the action of these laws, might not the process go 
on and the globe at length become so entirely 
changed that the particles of matter at the equator 
should fly off, and thus the whole mass be disin- 
tegrated and diffused in Space ? 

Let us look at this for a moment. You are all 
aware of the fact that the Earth is depressed at the 
poles and protuberant at the equator — that the mass 
of matter composing the body of our planet is heaped 
up, as it were, at the equator, and that the radius 
of the Earth at that point is 13 miles longer than at 
the poles. How was this figure obtained, and how 
comes it that it is not destroyed? 1 will attempt 
an explanation : 

By the rotation of every revolving body there is a 
force created called Centrifugal Force. This you 
see verified every day : not a carriage rolls along 
the streets but you see particles of dust flying off 



the revolving wheels. The same force is produced 
in the mass of the Earth itself. Now suppose we 
pass from the equator toward the poles. When we 
reach the poles we find there is no tendency to fly 
off from that point in consequence of centrifugal 
force, because there is no velocity of rotation. But 
as we recede from the axis of rotation, and as the 
radius becomes greater, the centrifugal force is in- 
creased in consequence of the velocity of rotation 
being accelerated. 
Now let us take the fluid particles upon the Earth's 
surface. What will be the consequence if it remain 
stationary, or if it move upward toward the equator 
and downward toward the pol&3?— for the solution 
of this question will determine the figure of the 
Earth, under certain limits of calculation. These 
particles, under the influence of the centrifugal 
force, have a tendency to fly off in a perpendicular 
direction, and the force of gravity has a tendency 
to draw them to the center of the Earth. Under 
the action of these two forces we find the particle 
does not remain stationary, but is moving upward 
along a central line upon the surface of the Earth 
toward the equator, and thus particle after particle 
is impelled upward. But how is it possible that 
this operation should ever cease ? I will explain 
the reason. 

When a body rests upon an inclined plane the 
action of gravity tends to bring it down that plane, 
and it requires a certain amount of force to heave it 
upward against the action of gravity. Now, when 
the particle of matter, under the influence of the 
combined forces already described, is heaved up and 
locates itself at the equator, still other particles are 
heaved up, till the whole figure of the Earth is 
swelled out ; and the next particles to be thrown up 
will ascend in some sense an inclined plane. Re- 
collect there is here a heaping up of matter — a 
swelling out — and the great level of the Earth is 
changed, and the time finally comes when the gra- 
vity due to the inclined plane upon which the par- 
ticle rests is precisely balanced by the force which 
tends to throw it up ; and, this equilibrium once 
obtained, any farther change in the figure of the 
Earth forever ceases. (Applause.) 

— We now take up the telescope, and with an in- 
quiring gaze examine the other planets. They, 
too, are moving upon their axes: But with the 
same velocity with which the Earth moves? No: 
They all have different velocities. Are their fig- 
ures in like manner changing by this rotation ? I 
answer: They are all changing ; or, if, not, they 
still possess a figure of equilibrium heretofore ob ■ 
tained. And we find, moreover, that there are 
certain narrow limits within which a figure of this 
character must be circumscribed — that if the velo- 
city of rotation given to any body should exceed 
a certain amount, this equilibrium is destroyed, the 
figure is changed, and even its solid substance dis- 
integrated and broken up. But in all the examina- 
tions we have been able to make, we find these 
narrow limits nicely resolved, and no one of these 
falling bodies has exceeded the limits of stability 
and perpetuity. 

Having examined the effect of Gravitation, I 
propose to trace out, for a short time, some of the 
effects produced by this extraordinary change of 
figure, if I may call it a change. (I do not know if 
it ever were different.) It is found that a globe will 
attract precisely as if the matter belonging to it 
were compacted at its center; and were all the 
planets precise spheres, then the Problem of the 
Solar System would have been merely to ascertain 
what shall be the relative influence of one of these 
bodies upon the other, all being regarded as simple 
material points. But this is not the fact : they are 
spheroids, flattened at the poles ; in consequence 






Astronomy. 



13 



of which we find a train of results of a curious and 
complicated character. 

When you look out upon the North Star, you find 
that object apparently fixed and permanent — and 
if the idea of fixity has ever entered jour minds, 
you can get no stronger conception of it than that 
which results from the fixity of this star. " As un- 
changeable as the North Star" has grown into a 
proverb. But if you could revisit this Earth 12,000 
years hence, and look for your favorite bright and 
beautiful star — lo! it has changed its position — it 
has wandered to a distant region of the heavens — 
it is no iooger in that point to which the Earth's 
axis is directed, or near it ; but some other has ta- 
ken its place. What can be the meaning of this ? 
I answer it depends up;n the figure of the Earth, 
and upon the action of the Sun and Moon upon the 
protuberant matter girdling the Earth's equator. — 
Now for the explanation of this curious phe- 
nomenon. 

It it were possible for us to extend the equator 
of the Earth till it met the Sphere of the Heavens, 
then to-describe around the heavens a circle of fire 
that we could discern, running all the way around 
among the fixed stars, we should have the curve 
called the Equinoctial in the heavens. Now, if we 
conld face out the track of the Sun among the 
fixed stars, we should find another circle, but one 
not coinciding with the one we have already loca 
ted, — they would form a certain angle, crossing 
each other at opposite points. The first of these is 
the Equator, tbe second the Ecliptic; and their in- 
tersections at their opposite points are called the 
Equinoctial Points. These points ha^e been 
and will be examined with the utmost scrutiny. — 
The attention of tbe earliest Astronomer was 
directed to their position in the heavens ; and npon 
the day in which the Sun, sweeping around in its 
orbit,crossed this othercircle called the equinoctial — 
on that day it was found that the length of the day 
and the night was precisely equal. Upon no other 
day did this occur except on the two occasions, 
when the Sun was in the act of passing through 
one or the other of these points, it became, then 
a matter of the deepest interest to locate this point 
among the fixed stars. I shall not attempt to 
point out the manner in which it was accomplished. 
It was simply with the brazen circles they had 
made for that purpose, that they accomplished this 
most desirable object. In Egypt great attention 
was fdven to this point, in consequence of the fact 
that they marked some great events, such as the 
overflowing of the Nile, by tbe heliacal rising of a 
certain bright star. In centuries after, by referring 
this star to the equinoctial points, the overflowing 
of the Nile came but the star which always an- 
nounced it did not come down in the horizon. 

What could be the meaning of this? Either 
one of two conclusions must follow. The star it 
self had moved, or the equinoctial point to which 
it was referred was moving; atd it was found, by 
referring all the stars to this point, that it was ac- 
tually moving in tbe heavens, going backward as 
it were, to meet the San; and in consequence of 
this movement, the Sun reached the equinoctial 
point before it otherwise would. Thus the differ- 
ence of time in the Sun's arrival at tbe equinoctial 
exceeded their computations, obliging them to carry 
forward the equinoctial points : and hence the term 
— Precession of the Equinoxes. 

You may ask what has this to do with the move- 
ment of the North Star, or the pole of tbe Earth. 
I will explain : The point called the North Pole is 
that through which the Earth's axis would pass if 
it were protracted so far as to meet tbe Celestial 
Sphere. This imaginary axis of the Earth is as 
fixed and permanent as if it were a bar of iron 



driven literally through the Earth, and extending 
out to the heavens in such a manner that its ex- 
tremities should rest in sockets and upon it the 
Earth should revolve. Now follow me : Take hold 
of this iron axle and heave it up so as to charige its 
position. What is the effect ? The equator is al- 
ways perpendicular to this axle, and if we shift the 
latter in the slightest degree we will in like degree 
shift the plane of the equator; and this first circle 
of light which we have supposed acrossthe heavens 
— the equinoctial — is ever changed as you change 
tbe Earth's axis. And whatever change is exhibited 
in the position of the equinoctial in like manner will 
be exhibited in the movement of that point called 
thePoleof tbe Heavens. But, in the process of time, 
we find that the point which tbe circle of the Sun 
describes through Space, intersecting the ecliptic, 
revolves entirely around ; and if that be the case, 
then must the Earth, in like manner, be governed 
and guided by this movement and revolve entirely 
around the ecliptic. And such is the fact. No less 
than 25,860 years are necessary to accomplish this 
mighty revolution ! But it is moving on ; and, 
from the earliest period down to the present time, 
we find this morion has been subjected absolutely 
to the Law of Gravitation, and that all this compli- 
cated result is a consequence of tbe oblate figure of 
the Earth. Had our globe been an exact sphere, no 
precession of the equinoxes would have been 
known — no change of position of the pole ever 
would have been marked ; but from century to cen- 
tury it would have held its place — permanent — un- 
changeable — fixed as the seal of Fate. 

Bat for the explanation of the causes of these 
changes : [The Sun and the Moon exert a constant 
force of attraction upon the Earth according to their 
masses and their distance. Were the Earth a per- 
fect sphere, the effect of these forces would be 
equable and producing no perturbation in the 
Earth's movements: But the pre pondering matter 
heaped up at the Earth's equator, and standing in 
a position which brings it at an obiique angle to 
the forces of the Sun and the Moon produces a dis- 
turbance of the rotation and a tendency to draw 
down the equatorial ring to a coincidence with the 
plane of the ecliptic. But this force is counterbal- 
anced by the rotary motionof the Earth, and while 
the equatorial ring endeavors to revolve about an 
axis in its plane it is alsoforced toward a revolution 
around an axis perpendicular to that plane. The 
result is, it revolves around neither of these axes, 
but on one which divides tbe angle between the 
two ; and by this revolution the pole of the Earth 
is as it were vibrated, and describes a small circle 
in the heavens. This nutation or vibration of the 
Earth has the effect of retarding it in its orbit, so 
that at the end of the year it has not completed its 
journey around the San, and, therefore, does not 
cross the ecliptic in exactly the same place it did 
before. The consequence is, the heavens and all 
the host of stars appear to us to be rolling slowly 
forward — that the equinox goes forward to meet 
the Sun — and hence the term Precession of the 
Equinoxes. The fact is, the Earth falls shortof her 
full revolution 52'' 110 (fifty-two seconds and one- 
tenth) in a year; and as there are 3,600 seconds in a 
degree, and 360 degrees in the great circle of the 
ecliptic, it follows that 25,868 years must roll round 
before the equinox will make a complete revolu- 
lution of ecliptic, producing within that period the 
longest and shortest day in tbe year on every day 
from the 1st of January to the 31st of December. 
This surprising effect is all produced by the com- 
paratively insignificant superabundance of matter 
aggregated upon the Earth's equator. j 

But let us look at another point. We find that 
Earth is not entirely solid, its surface is covered by 






I 



a fluid with a tmrite — and the inquiry arises 

-is fluid . — whether there are 

le ocean cannot pass. 

ly not occur that under tfa influence 

tides may 
which shall sweep :~er and submerge the 

-- surface of the ha .:be? Is 

aeain. there are here provisions which m: 
wisdom of Him? I: i: were 

te up our ocean and to er: 
jf the planet Saturn, nc would 

ensue — the ocean wonld ove : bounds to 

which we worn i it, and rush 

from one ~er to the c 

in its path : hut the re 

d the spec : cean, 

we find the are complete; a: 

the action is going en ::„ ; ~ j — Ufa* igh the 

. : are caused to leap np in sor_ | Dward 

the Moon and the Sun. yet there is a limit beyond 
which they ear_- 

There are many who find it exceeding difE: 
understand the nature of Tides, and how it is that 
the Moon and San should produce them. The fa i v 
ing up of the water on the side nest to the Sun and 
Moon, is a matter easily comprehended ; yet how 
these bodies should produce a tide on the opposite 
side is quite mysterious. But let U3 examine this 
question and3ee whether an explanation cannot be 
had. The cause of tides is : rion of the 

Moon uoon the mass of water on t s sur- 



5fi '.":'.•:'."--.- -:e are certain elements, 

as they are called, which dx and determine the na- 
ture of the orbit of a.: 

:h it becom e s nee essary to explain 
what these elements are. 

In the first^ place, the ellipt a certain 

figure determined by a longer diameter called its 
. and a shorter called its shorter axis. — 
When their lengths ignre of the el- 

lipse can be describ-: - thing — to 

get the magnitude of the orbit — but when that is 
:d we do not yet know what location it takes 

ects. In order 
- we must get the direction of this 
longer line calk 3 at s vis. Now fhe Sun is 

always located at the focus, and the distance of the 
Sun Go :ine longer axis is on one side the 

shortest and on the other the longest possible dis- 
tance. Having, then, the ist line,, and 
d to the fixed plane, we are 
enabled to locate the orbit in Space. We have yet 
to obtain the periodical time, and not only the pre- 
cise position of the planet in some one known point 
in its orbit, but the particular date; after which we 
are enabled to follow its movements in all its wan- 

. m we have accomplished this, the question 
: Are there no subsequent changes ? There 
are changes of a most curious and complicated kind, 
and which in the outset would seem to destroy ab- 
solutely the nature of the orbit I to the ul- 



face, drawing it upward toward itself. If every I timate des:. the entire System. In the 

- e were e J from the Moon, then would Moon's orbit we find that the point nearest to the 

the action be the same on every one there Barth, called the Moon's perigee, is never fixed and 



would be no eh : but the truth is the 

le quantity 
pared distance: the distar.ee nftbe 

Moon is but 30 times the diameter of tfl e E 
the water on the side Dext to the Moon is 
than that on the opposite side, and hence the 
stronger attraction ea on that side nearest 

the Moon. 

But to render the explanation more r srfect, let 



permanent, but always varying its position, and 
performing an entire revolution. This is a 
point to which Newton directed his mind, attempt- 
ing to account for the rapidity with which this line 
rvolvingin the heaveris upon the hypothesis 
..ion. He brought into account as he 
supposed, every point that could bear upon the 
result, and when he reached it, he found the amount 
of cha: ant with that actually ex- 



OB gi the position we took some time since"! hi - e. Here the Law of Gravitation 



regard to the tact that the Moon was ever 
falling toward theBa ... This I have attempted 
and I hope it was comprehended. You 
Will understand also that the E 

toward the Moon under the action of precisely the 
same power. N 3 could see a mass of fluid 

in the act of falling toward a body, we would ob- 
serve the attracting body operate more s:. 
upon the particles next to itself, and draw t. 
away from the re; an behind in their | 

race" to the center: hence we see e 

waves next to the Moon should be protuberant. Bat j 
how is it that those on the opposi" . led 

out? Because theEi 2 oon 

than the ocean on the opposite side, is drawn a~ 
toward the Moon and leaves the ocean behind; 
hence it is protuberant in both directions. — But I 
not intend to go into a full exposition of the tides ; 
I must pass on to other matters. This has been a 1 
most difficult problem for the Mathematician. Tt : 
combined action of the Moon and San. and their 
coming in opposite directions, producing extraor- 
dinary' changes. — then the fact that these are not 
revolving in the same plane and not at ail in the 
plane of the E arte s equator, causes them to sink on 
one side and bear up upon the other side. In all 
the computations of these varying influences, the 
res -its have nearly : incided with the actual facts. 
I propose, in the next place, to examine effects 
produced upon the Moon's orbit by the disturbing 
action of the Earth. And here I shall have occa- 
sion to reveal to you some extraordinary niove- 
^ s -ts that belong to the whole System by which 



seemed at fault ; and after many tedious efforts, 
this great man ~ied without solving its 

ry. It was taken up afterward by his suc- 
cessors, and in every instance it seemed that New- 
ton's results were confirmed most absolutely. It 
was fir :n up to Ciairaut. who grappled it 

with ail the power of analysis : but, in spite of all 
be could do, he reached jast the results attained 
nis predecessors ; and, for a moment, he de- 
it was impossible to account for this curious 
exhibition in the heavens. But strange as it may 
appear, an individual without education in Astron- 
omy, with simply a knowledge of Mathematics, 
stepped forth and ventured to defend the Law of 
Gravitation — and there was a long dispute between 
the two — one of them a Metaphysical Pm osopher, 
j and the other, one who had devoted his best ener- 
j gies to the cultivation of pure Abstract Science. 
; Ciairaut determined to prove himself right j re- 
1 d his entire investigation, and finally in the 
j examination of a mathematical series, entering in- 
:. the result, which at each successive term had 
: grown less and less till it seemed that they were 
! absolutely to disappear, and he believed they 
! would disappear, and that the remaining ones 
might be neglected j he found, on pursuing the 
problem a little farther, that the character of the 
terms began to change, and instead of diminishing 
they began to increase, so that when he had added 
together all tee terms and completed the result, he 
found the Law of Gravitation was confirmed in the 
r solute manner — Theory and Observation co- 
inciding precisely. Applause, j 



Astronomy, 



15 



I would call your attention to another single in- 
vestigation, which has, in like manner, demon- 
strated not only how far the human mind can carry 
its researches,*but how absolutely applicable this 
one solitary law is to all the changes and phe- 
nomena which are exhibited by these heavenly 
bodies. I have already told you that we have records 
of eclipses extending back 2,500 years. Now 
when we come to examine the velocity with which 
the Moon was moving at that time, we find that it 
is not the same with which it is now moving ; that 
it is actually in advance of the position it should 
occupy — on the hypothesis that its motion is uni- 
form and was accurately determined at that time — 
by an amount equal to nearly four times its diame- 
ter. It seemed impossible to account for this ac- 
celeration of motion. Every effort was made to 
reduce it to the La*v of Gravitation; but it seemed 
to evade every attempt. Some were disposed to" 
reject the early observations ; others believed that 
there was a resisting medium which impeded its 
motion, diminishing its distance from the Earth, 
and accelerating its motion around the Earth, de- 
scribing a spiral line, and that slowly and surely it 
would at length approach our globe and bring de- 
struction to the whole System. 

In this dilemma, La Place comes in to the rescue 
of Physical Astronomy. He took up this problem, 
and with the aid of the accuracy he had obtained 
in his previous investigations, he finds himself able 
to master it, and not only to do this but to tell the 
reason why it was that this accelerated motion of 
the Moon was going on. I will attempt his expla- 
nation: 

It is found, on examination of the elements of 
the orbits of the planets, that this longer axis, 
which been described, is invariable — it never 
changes — while the shorter axis is subject to fluc- 
tuation according to the configurations of the 
heavenly bodies. It is found that the E arth's or- 
bit is chaning its figure. It is now eliptical ; but 
this is slowly disappearing. It has been going on 
for centuries, and must continue for centuries to 
come, till finally the shorter axis becomes equal to 
the longer, the eccentricity of the orbit disappears, 
and the Earth revolves in a perfect circle around 
the Sun. When this point shall have been reached, 
analysis demonstrates the truth that a change be- 
gins and the figure then circular, slowly begins to 
come back again to its elliptical figure : and thus, in 
periods so great that the human mind cannot 
stretch sufficiently far to comprehend them, we 
find these mighty oscillations sweeping backward 
and forward in the narrow limits within which 
Infinite Wisdom has confined them. 

But what effect should this changehave upon the 
motion of the Moon? I will answer. The Moon is 
revolving about the Earth, and its motion is im- 
pressed upon it. Now, if no other object existed 
outside the Moon's orbit, the Earth would be 
able to draw the Moon closer to itself and impress 
upon it a central movement. But all the other 
heavenly bodies are on the outside of the Moon's 
orbit drawing it away from the Earth, taking it 
partly from under the influence of the Earth and 
exerting their influence upon it. Hence, if it were 
possible to remove the Earth and the Moon farther 
from these disturbing influences, then will the Moon 
come entirely under the influence of .the Earth, and 
its motion will be increased. Now this is the exact 
case in Nature : it is precisely what is going on, in 
consequence of the changes on the figure of the 
Earth's orbit. Its orbit is becoming more nearly a 
circle, not bringing the Moon so near the Sun as it 
once did ; hence it is able now more effectually to 
master its own satellite and thus impress upon it 
a more circular orbit. 



But is this to go on throughout Eternity 1 I an- 
swer, No. For when an orbit shall have attained a 
circular form and begins to recede back to an elliptic 
figure, then will these changes again take place in 
the motion of the Moon, and that which was 1 once 
acceleration become retardation and from the effect 
of the very same cause, the Sun will begin to take 
hold of the Moon with greater and still greater 
power. Now what the period of these changes 
may be — although possibly within the limits of cal- 
culation — we have not yet computed. One thing, 
however, we do know — they are not to be reckoned 
by hundreds or by thousands — they must expand 
to millions of years before the exact conformation 
of the System can be brought about again. 

Thoughl have presented you demon strati on upon 
demonstration to night, you will pardon me if I oc- 
cupy a little more than my allotted time in giving 
you some account of the Telescopic Appearance of 
the Moon's Surface. Those who for the first time 
behold the Moon's surface through a powerful in- 
strument, will always be disappointed in its appear- 
ance. There are mighty mountains on its surface ; 
there are deep bleak cavities, some perhaps fifteen, 
twenty, forty and even sixty miles in diameter and 
sinking below the surface seven and eight thousand 
feet. Out of these, mighty rocks arise two thou- 
sand feet above the level of the valley, casting their 
deep black shadows upon the plains below. All 
these things are very fine ; and yet on looking at 
them through the telescope for the first time, one 
is invariably disappointed. You cannot see moun- 
tains as you see them in the Highlands of New- 
York: you cannot see the gray rocks projecting so 
beautifully as you behold them on some earthly 
mountain hight. Remember after yoar telescope 
has carried you out as far as it can reach, there is 
yet a whole hundred miles to be overcome. So in 
spite of all you can do, and with all the aid you can 
bring, you are a hundred miles from the object. 

But do we know nothing of the Moon ? Are we 
so far off that we can tell nothing of the character- 
istics of its surface? I answer: We know that 
towering mountains lift their lofty heads, deep cav- 
erns yawn, and there are vast circular elevations 
resembling the usual productions of volcanic ac- 
tion. And how do we determine these things? — 
By the lights and shadows which show themselves 
to the eye we measure the hight of these moun- 
tains, by remarking the relative position of the Sun 
and the Earth. We mark the extremities of their 
long deep shadows and find that as the Sun slowly 
rises, the shadows by degrees recede toward the base 
of the mountains ; and when noonday arrives they 
entirely disappear. Then as the Sun begins to decline 
on the other side, the same dark shadows are east 
in the opposite directions. We watch these move- 
ments till we ascertain with perfect certainty the 
character of the object which casts the shadow, 
and we measure its hight. These are reliable facts. 

But the question next comes : How is it possi- 
ble to measure the depths of those deep cavities ? 
It appears as if immense lakes had once filled 
them, and by some extraordinary means the water 
had been evaporated, leaving the interior dry, hard 
and sterile. We find these depths in like manner 
as we ascertain the hight of mountains. When 
the Sun is first rising it casts its light into these 
cavities of the Moon ; we see shadows cast by the 
sunward sides, and the limits of the cavities are 
defined with a degree of accuracy surpassing any- 
thing upon the surface of the Earth. For the shad- 
ows are not here so black as upon yonder orb. — 
They are mitigated and dispersed through the in- 
fluence of our atmosphere. But on the Moon there 
is no atmosphere, at least not such a one as will 
compare at all with ours. The Moon's atmosphere, 



16 



Prof. Mitchell's Lectures. 



if indeed it have one, can be no denser than the 
extremely rarified air left in the most perfect va- 
cuum yet produced in an exhausted receiver. It 
cannot sustain animal life — it cannot support clouds 
nor can it sustain combustion. And, for the reason 
that the Moon has no atmosphere, there is no grad- 
ual fading away of the light as the San sinks deep- 
er below the horizon — nosofc, mild and lovely twi- 



light, such as sheds a holy serenity over our favored 
globe — but instantaneous and appalling darkness 
follows the setting of tbe San, drear as the nightof 
Death; and broken — not by the "rosy fingered 
morn," slowly waxing from' faint streaks of light 
to the fallness of the day-spring— but startled from 
the very depth of blackness by the lightning-flash 
of the San's meridian glory. (Applause.) 




LECTURE IV. 

Brror of Supposing Gravity the Cause of all Motion Rotary and Orbitical Motion Inclination of Planes not 

caused by GravityNecessity of Present form of Our Sysrem for its Perpetuity.... Pertuibatinns.... An Hour of 

Eternity Weight of Placets— How Calculated— La Place's Measurement of Jupiter.... Ratio of Planetary 

Distauces.. ..Vacuum between Mars and Jupiter — Sus( icons of a planet there — Discovery of the Four Aste- 
roids— Theory of their Origin — Force Necessaiy to Break, a Planet in F agments— Discovery of a Fifth Asteroid 
— of a Sixth— of a Seventh -of an Eighth. ...Tne Planet Jupiter Ga'lileo and the Ptolemaian School.... Dis- 
covery of Velocity of Light by Jupiter's Satellites \berration of Light from tbe Fi»ed Sc-*rs caused by Mo- 
tion of the Earth — A Proof of the Velocity of Light— Effect of the Star's Motion upon its Rays another Proof 
....Struve's Attempt to Determine the Velocity of Light. 



[In consequence of the impatience of the audience, 
occasioned in part by the time-piece in tbe Tabernacle 
being considerably toofa6t, the Lecturer was called out 
sooner than usual, and before the Reporter had taken 
his seat; consequently the substance only of the first 
two or three sentences can be given. The Professor 
was proceeding to show that the general supposition that 
ell phmomena are accounted for by the laws which are 
at present known is not true ; and for the following rea- 
sons:] 

In the first place, we find that all the planets of 
which we Wave any knowledge, are revolving upon 
axes and all rotate in the same direction on their 
axes that they move in their orbits. Now as the 
Earth is sweeping round the Sun, it is held sta- 
tionary to that great center by the Attraction of 
Gravitation; bat it would be held in its position 
even if it did not rotate upon it3 axis at all. Gravi- 
tation has nothing whatever to do with the rotation 
on its axis. Bat again : We find the Earth sweep- 
ing round the Sun in an orbit, the plane of which is 
located in a particular position in the heavens — 
Now, gravity would have held the Earth equally 
steady to this center, if that orbit, instead of sweep- 
ing in the direction it now does, had revolved in 
any other direction whatever, forming any p'ossible 
angle with the present orbit. Once more : We 
find all the planets revolve about the Sun in planes 
nearly coincident, traveling on in nearly the same 
direction. Gravity had nothing whatever to do 
with the inclination of their planes, nor with the 
starting of these planets in their orbits. If they 
had revolved in contrary directions gravity would 
have held them just as perfectly; and irjdeed we 
find a full confirmation of this truth in the fact that 
tbe comets which come in from every possible sec- 
tion of the heavens, observe no particular direction 
either in the position of their orbits or the manner 
in which they sweep around the San. Tney, too, 
are governed, as are the planets, by the Law of 
Gravitation. 

Now the question arises at this point : Is there 
no Evidence of Design in the Structure of our Sys- 
tem, that it was built in this way ? Why do not 
all planets sweep in any direction at all consistent 
with the Law of Gravitation, and having their planes 
inclined in any possible way, as the comets? I 
will answer it, and I think in a way satisfactory to 
every mind. If the System had thus been con- 
structed, it would have contained within itself the 
seeds of its own destruction : it never could have 
endured ; the time would have come when tbe 
planets would have rushed madly from their 



spheres and the whole System have been swept to 
utter destruction. We find that in order to pre- 
serve tbe stability of this beautiful System, it is 
necessary that these planets should revolve in the 
same direction, and that the planes of their orbits 
should be nearly coincident with each other, and, 
farthermore, that the Law of Gravitation has 
nothing whatever to do with the localities of the 
planets. Suppose, for example, that Jupiter could 
be' snatched from its present orbit and could occupy 
that which the Earth now occupies, and we could 
throw the Earth out to fill the mighty orbit of Jupi- 
ter: Gravity would hold each of these equally 
steady. But then, even were all other bodies to 
move on in the position they now do, or in any 
combination which now exists, such an event 
would produce destruction. It is not possible to 
change places with any of these bodies and at the 
same time preserve the stability of the whole Let 
us then mark the difference between what is abso- 
lutely dependent, and what is not dependent opon 
these laws : And in this difference we see that an 
Almighty Power has adjusted this vast machinery, 
and that it has been formed in Infinite Wisdom 
and with Infinite Skill. 

With these views I shall proceed to the exami- 
nation of the System with reference to those bo- 
dies recently discovered. But before I proceed it 
will be necessary to make some explanation with 
regard to certain matters involved in this discus- 
sion. And first, this matter of Perturbation. I 
know this subject is somewhat difficult to under- 
stand ; but a few words, I think, will be sufficient 
to render it quite plain. Suppose the San to be 
located at a given point; at a distance equal to the 
shortest distance of the planet Mercury from the 
San we locate that planet: this is irs perihelion. 
Next let us place Venus; then the Earth ; and so 
on with all the planets, — all located in a right line 
and in their perihelion, or nearest position to the 
San. Suppose they receive the primary influ- 
ence which starts them on their mighty journeys. 
Now will they all come around again to occupy 
the starting point after a single revolution? No. 
Will these perihelion points remain in a right line 
after the first revolution ? No. The very moment 
they start they begin to operate opon each other 
through the force of attraction, and all the elements 
of every orbit begin to be swayed backward and 
forward. These changes are going on perpetu- 
ally, — these perihelion points are moving onward, 
their eccentricities continually changing ; and mil- 



Astronomy, 



17 



lions of millions of years will roll round, when at 
length — at the expiration of some mighty and al 
most inconceivable Cycle, when this great Time- 
piece of Eternity shall have struck one— they will 
all occupy their original relative position and once 
more start on their immense journey. (Applause.) 

Now, this heing the case, how is it possible for 
the human mind to reach to any knowledge of the 
influence of these bodies mutually on each other? 
for if the limits of their orbits are continually shift- 
ing, there must be some difficulty in getting at that 
influence; for before you can make any use of es- 
tablished positions they are changed again. This 
is all literally true : and the Astronomer is obliged 
to seize every one of them; and even the San him- 
self, and weigh them all in a balance: he is 
obliged to ascertain the amount of matter belong- 
ing to each and all of them ; and when he shall 
have attained to this knowledge, he must then com- 
pute the influence which each exerts upon the 
other, and thus with long and patient toil trace out 
all their devious wanderings. 

I shall now attempt to explain how it is that the 
weight of these distant orba is determined. How 
can we weigh this Earth against the Sun? How 
can we place them as it were in some mighty bal- 
ance and ascertain precisely how much one prepon- 
derates over the other ? Follow me, if you please, 
in a very brief exposition of this problem. In the 
first place, the power of gravitation upon any body 
is determined, as all know, by the amount of ve- 
locity it is capable of producing in a falling body in 
one unit of time. If at the Earth's surface a body 
falls 16 feet in the first second of time, that is the 
measure of the intensity of gravity at that point. — 
But if this Earth did not contain the amount 
which is now in it — if it were smaller, a body 
would not fall so far in a second of time. — 
There is a certain law establishing this, which we 
have ascertained. I have already stated that the 
Moon is ever falling toward the Earth, and the 
amount by which it falls is measured — we know it 
exactly ; hence we know precisely the influence 
exerted upon the Moon by the Earth — and that is 
the first point. Now suppose, on the opposite side 
of the Moon there was another Earth, and it were 
as large as ours and equally distant, but con- 
tained double the weight of matter. At the same 
distance it would produce twice the effect of our 
Earth. Increase its magnitude tp three times and 
the effect is increased in like 'proportion. Now 
there is no such other Earth, but there is the Sun, 
and let us attempt to ascertain the compara; 
tive weight of the Sun and the Earth, by weighing 
the amount of action which each exerts upon the 
Moon. In the first place, then, the Moon is attract- 
ed by the Earth and is caused to fall through a 
certain distance in a given time. Secondly, the 
Earth itself is attracted by the Sun and is caused 
to fall through a certain space in the same time. 
Now with reference to the magnitude of the Sun, I 
think the Moon and the Earth may be regarded 
as equal. It is exactly like dropping two weights 
one of one pound and the other of two pounds to the 
Earth; they will both fall with the same velocity. 
So with the Moon and the Earth: the difference of 
their masses may be regarded as absolutely nothing. 
Now the Sun deflects the Earth from a tangent line 
by a certain amount which measures its influence 
upon the Earth; likewise the Earth deflects the 
Moon by an amount which measures the intensity 
of its force upon that satellite. The amount of 
deflection produced in the orbit of the Earth is more 
than double that exerted by the Earth upon the 
Moon : Hence if the Sun were equally distant from 
the Moon with the Earth, it should be twice as 
heavy as the Earth, because it produces twice as 
2 



much effect. But the truth is, it is not at an equal 
distance — it is 400 times farther off. If then nt this 
distance it produces twice the effect of the Earth 
itself, we must increase it in the ratio of the square 
of 400, or 160,000, this number must be multiplied 
into the exact ratio of the influence of the two 
as already estimated at an equal distance, which 
carries it up to 354.436 earths ; and that is the pre- 
cise ratio existing between the mass of the Earth 
and the Sun. Thus it is that we are able literally 
and absolutely to weigh these bodies one against 
the other : Hence every satellite which revolves 
about its primary planet, gives us the means of 
weighing that primary. 

But what is to be done in cases where there are 
no satellites? Here the problem is more difficult. 
The influence exerted by other planets on these 
bodies in swaying them from the paths which they 
otherwise would have pursued, tells us the amount 
of matter belonging to them. In this way Astrono- 
mers have attained to a most accurate knowledge 
of the value of the mass of all the planets. 

It is true that in the instance of Jupiter, La Place 
in his earlier computations made it out different 
from subsequent discoveries. He said that it would 
require 1067 Jupiters to make a mass equal to the 
Sun. He reached this conclusion from a series of 
observation made by the Astronomer Puond, and 
when he had examined them all critically he said 
that the mass could not be in error by one hundredth 
part its value and that the chance of its varying to 
that amount was as eleven millions to one. He had 
brought all the powers of analysis itself into the 
calculations, and the probabilities of his being in 
error were as I have stated. But it seemed as if 
Chance was not to have its peculiar dominion in- 
vaded in this way, and, if I may be allowed to use 
the expression, Chance determined to chastise the 
hand that had ventured to draw aside the curtain 
and unveil her mysteries ; for it has been proved 
most positively that that one chance out of eleven 
millions was the one that turned up, and La Place- 
was wrong. (Applause) The fact was, the meas- 
urements had been made indifferently and a long 
time ago. He had used a computation made upon 
a little body called Encke's Comet, and from the 
ethereal mass of the elements of this ghost of a 
world, so filmy that it has not ihe power to lessen 
even thelightof the smallest stars that shine through 
it, he had made his calculation of the mighty orb of 
Jupiter. The mass of Jupiter, as computed by La 
Place, was employed to determine how much dis- 
turbance existed there, and there was not enough. 
So when this mass was applied to other calculations 
and suspicions were - aroused that it was inac- 
curately calculated, it excited other measurements, 
until at length all agreed very accurately in giving 
the mass of Jupiter such, that 1049 such bodies , 
would make one Sun. 

We proceed now to the Structure of our System. . 
It will be remembered by all who heard me in my 
Second Lecture, that the older planets were for a 
long time known. They are arranged according to. 
a very curious law, with reference to their distance 
from the Sun. It is known, for example, that when, 
passing out from the Sun to Mercury, and from, ' 
Mercury to Venus, there is a certain ratio of dis-- 
tance, which holds true in regard to the dist3/iy&& 
of the other planets, for an immense space of 
350,000,000 miles, until you come to a mighty gulf, 
within which no planet was known to revolve ; and 
the moment that limit was passed, the old law was 
resumed. This curious law was detected by Bode. 
I will explain the law in a simple manner. Be- 
ginning with the first of this series as nothing, and 
assuming 3 for the first distance, we have the fol- 
lowing series : 0, 3, 6, 12, 24, 48, 96, and so OQ» 



18 



Prof. Mitchell's Lectures. 



This is obtained by multiplying each succeeding 
term by two. Now, if joa add 4 to every term 
of the series., you have another series as follows : 

Mercury. Venus. Earth. Mart. Jupiter. Saturn 

4 7 10 16 28 52 100 

and so on. This latter series represents most accu- 
rately the distance of all the planets from the Son. 
But in passing from Mars to Jupiter the link was 
broken — there was no planet to fi'l up the space 
— and when Baron De Sac detected this law, and 
found it to be perfect in every other instance, he 
came to the conclusion, and could not resist the 
conviction, that a planet unknown revolved in 
that space. Such was his absolute conviction, that 
he actually commenced a computation of its orbit in 
1734. He made out its distance, and published 
the elements of its orbit, fifteen years before any 
bodies were known to exist in that space. In 
the year 1800 such was the effect produced by 
his investigations, that a Congress of Astrono- 
mers met at Lilienthal, to unite upon a plan for 
hunting down this unknown body. They agreed 
to divide the whole region into zones, twen- 
ty-four in number, or one to each Astronomer. 
They commenced their labors on the first day of the 
first year of the present century, and before they 
had hardly commenced, oge of their number de 
tected a small star which did not exist on his chart, 
although he had laid down upon it, as hesupposed, 
all the fixed stars. H s name was Piazzi. of Paler- 
mo. With what anxiety did he wait till the fol- 
lowing night again to examine this stranger! — 
When the next night came round, to bis inexpres- 
sible delight he found it had changed its position, 
and was actually retrograding as a planet ought to 
do. But he did not venture to believe he had so 
soon discovered this unknown wanderer, and only 
told his friends he had found a very suspicious 
body and supposed it might be a comer, but he 
could not tell — it looked very much like a planet. 
Baron De Sac, when he heard of this discovery at 
once seized it, saying: "This is my planet which 
I have so long predicted." He took a tew observa- 
tions, but in consequence of the fact that it soon 
fell into the rays of the Sun, only a few observa- 
tions could be made, so that but for the extraordi- 
nary discovery of other bodies, by other observa- 
tions at short intervals it could not have been 
known to be a planet But Baron De Sac at once 
commenced a computation of its orbit. Tbey had 
all agreed in assigning to it exactly the place that 
should be occupied, in order to make the law of 
relative distance which had previously been 
thought to exist, apply in this last instance. Baron 
De Sac knew the planet was fouod, and when he 
compared his own investigations with those which 
were found to result from actual observation, it wbs 
discovered that he had predicted its place precisely. 

While all the astronomical world was rejoicing 
in the beautiful law and the complete establish- 
ment of the Harmony of the System, another object 
was found — another planet was detected which 
seemed to have an orbit precisely similar to the 
one already found. Here was a most astonishing 
anomaly — two planets revolving in orbits nearly 
coincident. The like was to be seen nowhere e'se 
in the entire System. What could be the meaning 
of this ? How happened it that these two little 
bodies occupied this place and with orbits so near- 
ly equal? Oibers conceived the idea that they 
were fragments of a former mighty planet which, 
by the action of some powerful force, had been 
rent asunder and scattered in every direction. — 
Strange theory this ! passing strange! But follow 
me through this curious history, and then decide 
if there be any foundation for its truth, or whether 
it is mereJy an astronomical dream, In a very 



short time, to the astonishment of the world, Hard- 
ing find* another planet. There are three. Oibers 
was confirmed in the opinion that his theory was 
true, and, said he, " if this convulsion did take 
place and the fragments were scattered, then, in- 
asmuch as they started from the same point, they 
must all revolve to t at same point in their orbits.'' 
If he could fi d the place where their orbits inter- 
sected or crossed each other, (which we have alrea- 
dy explained as the Nodes.) inasmuch as these 
were common points, it might be true such a dis- 
ruption had taken place. It was on this hypothesis 
that, after watching from night to night "and from 
y ear to year in the particular region of this node, 
tbey finally detected a fourth body. Here, at 
length, were four bodies revolving In nearly the 
same orbits, and thus the truth of this wonderful 
hypothesis was verified. 

Again, an investigation was made to ascertain 
the amount of force necessary to burst a planet 
and separate its fragments. Le Grange demon- 
strated that with a force 150" times greater than 
that given to a cannon ball the particles would 
sweep off in an orbit called the parabola ; but that 
the foroe of 20 times would give elliptic orbits of 
different degrees of eccentricity. There is also an- 
other point : In case this theory was true, the larger 
fragment wouid occupy more nearly the orbit de- 
scribed by the original body, and the smaller one 
revolve more obliquely to the plane of the ecliptic. — 
This was found to be the fact : in comparing their 
bodies and their orbits some of the smaller ones 
made an angle as high as 30 degrees, with the plane 
of the ecliptic, and had exceeded the plane of the 
zodiac which confines all the rest of the planets. 

W T hen they were thus fixed and determined, and 
aft^r fourteen years of examination all bad been 
done that it seemed could be done, and the investi- 
gations need not continue any farther with the 
hope of success, many years roll round and finally 
in Dec 1845, we hear announced that another of 
the asteroids had been added to the four: As- 
! traea, discovered by Encke of Dresden. He was 
j prosecuting this examination for the purpose of 
I finding the nodes of the asteroids and on the 
plane that had been previously adopted, having 
I more accurate charts of the Heavens with the 
i stars more carefully laid down. The moment he 
j detected a new star he suspected it of being a 
I planet, and a few evenings would always settle 
1 the investigation ; and in this way he detected 
: Astraea. For two years he continues, when lo! he 
! has found another planet, and Hebe is added to our 
System. But he had scarcely described it, when 
I Hinds, an Englishman, has fished up another, Iris; 
I and before we know the name given to this one, 
j the same Astronomer announces another, and Flo- 
i ra is joined to the other seven ! Thus we have the 
I beautiful phenomenon of a group of eight sisters 
j revolving around the Sun in orbits of nearly equal 
i magnitude, in periods absolutely identical; all oc- 
| cupy the center of the space between the Planets 
j Mars and Jupiter, and by their joint action, their 
joint mass, their joint distances, fulfilling thisbeau- 
| tiful law of Baron De Sac. 

Having gone through the examination of these 
j objects, 1 shall proceed to give an account of the 
Planet Jupiter. This is the largest in our System, 
and one of the oldest known. We have, indeed, 
no knowledge of the time when thi3 beautiful orb 
was unknown. Go back to the pages of history as 
far as you please — so even beyond the limits of 
tradition — still you find that this planet was known 
to the earliest inhabitants. How do we know this 1 
some wiii have already inquired. Let me tell you. 
If we go to the records of the earliest nations, we 
find invariably this curious fact: that the days of 



Astronomy . 



19 



the week, seven in number, are named after the 
planets, counting the San and Moon, thus — the Sun, 
the Moon, Mars, Mercury, Jupiter, Venus, Saturn. 
Every nation — the Cbiaese, the Egyptians, the 
Persians, the Chaldeans — have applied the names 
of the planets to the days of the week. They do 
not, to be sure, begin the week on the same day; 
but beginning with their first day, they run round 
the cycle exactly in the same order. There is but 
one way of explaining this remarkable coincidence, 
and that is : They must have received this from 
some nation anterior to either of them ; it must have 
come down from the same common origin. Hence 
we run back anterior to tradition itself to find the 
first discovery of these planets. 

In this beautiful planet, Jupiter, we find one that 
fastened the gaze of the earliest minds that turned 
their attention to the heavens, and by possibility it 
may have been detected before Venus ; for Jupiter 
is seen at all possible distances from the Sun. while 
Venus is always comparatively near. 

When the telescope was first directed to this 
wonderfal orb, a sight was revealed to the as- 
tonished gaze of old Gallileo, that seemed al- 
most to stupify his mind ; — there were four beau- 
tiful moons revolving about this noble orb, obe- 
dient to its attraction. You all remember that 
at the time this discovery was made the battle 
was raging between the old and new school of 
philosophers ; — those who believed with Ptolemy 
and those who followed Copernicus. Grallileo bad 
become a convert to Copernicus, stood up the 
champion of truth, and fortunately for the world 
armed himself with a power that all the antagon- 
ism of Earth could not withstand. " You tell me," 
said he, *' the Earth is the great center about which 
the Universe is revolving ; now I tell you that yon- 
der globe shows a miniature system like our own. 
and while we have a single moon, there is a planet 
which has no less than four. Do not then attempt 
to impose this impossibility upon me I do not be- 
lieve it." He combated those who opposed the 
progress of truth, till finally he incurred the dis- 
pleasure of the Church itself. You all know the 
fact, that, borne down by the weight of years he 
was brought before the Inquisition and forced to 
recant his opinions in the most solemn manner ; but 
such was the power of truth that in spite of all the 
threatening by which he was surrounded, as he 
rose from his knees he stamped upon the Earth and 
said, "she does move though." (Applause) 

It seems that Jupiter and its satellites were 
given for a most valuable purpose, and I ask your 
attention to but one or two of their uses. And 
iirst, the fact that they served to determine the 
velocity of light. I know many minds revolt from 
the conclusion which Astronomers have reached, 
when they say that light flies twelve millions of 
miles in a minute, and that there are objects so dis- 
tant that their light would require the enormous pe- 
riod of fifty thousand years to reach our Earth. In 
the language of my ' old friend ' — " this is a hard 
story " It is incredible ; but before this Course of 
Lectures closes 1 intend to show clearly and posi- 
tively bow this has been determined and how much 
reliance is to be placed upon this wonderful revela- 
tion. 

Previous to the discovery of the satellites of Jupi- 
ter, and their eclipses, it was believed that light 
passed instantaneously over the most distantspace. 
It was believed that if a lamp was lighted and the 
eye could see it through a space of millions of 
miles, that the instant it was lighted the eye, if 
directed toward it, would see the light. On the 
discovery of Jupiter's satellites, they were found 
revolving in such orbits that in every revolution the 
three interior ones were always eclipsed and dis- 



appeared from the sight. It did not require a long 
series of observations before the Astronomer be- 
gan to predict the coming of their eclipses as we 
do those of the Moon. He examines the result of 
his computation, and after a while detects a cer- 
tain amount of discrepancy between the observa- 
tions at the two opposite points of its orbit. — 
He tries again, but in spite of all efforts, after 
long years of toil, he could not reconcile the' 
predictions exactly with the observations, and 
then he began to inquire if by possibility 
there could not be a law which would recon- 
cile them. Let me endeavor to show how this was 
attained. Suppose the Earth to be at a given 
point in its orbit, and Jupiter to be in that part of 
its orbit on the same side as the Earth: the dis- 
tance which separates them is precisely the differ- 
ence of the distance of their orbits from the Sun. — 
But let the Earth revolve around to the opposite 
side of the Sun and Jupiter remain as before: the 
distance is now increased by the whole diameter 
of the Earth's orbit — 190,000,000 miles. Now the 
observer on the Earth, when nearest to Jupiter, 
will, in the eclipse of its satellite, see the light 
disappear too soon according to the computation. 
Why ? Because the stream of light is shorter by 
an amount equal to the whole diameter of this or- 
bit, and consequently runs out more quickly. — 
When he takes his observation from the opposite 
side of the Earth's orbit, he finds the eclipse comes 
on too late, because the stream has 190,000,000 miles 
farther to run, and of course he will continue to see 
the satellite till the stream runs out. Now then, in 
this way we are able to determine bow long it 
takes light to pass across the Earth's orbit. Then 
by ascertaining the exact difference in these ex- 
treme points, this single calculation of the velocity 
of light would account for all the discrepancies, and 
reconcile theory and observation in the most per- 
fect manner. But to pass across this orbit requires 
sixteen minutes ; hence the velocity must be at 
the rate of 12,000 000 of miles in a minute. 

Here, then, is the foundation upon which this 
res uk was first rested. "Well," some skeptical 
mind will say, " that is only a single observation; 
give me confirmation of it from some other sources, 
or I must reject so astonishing a result." For a 
long time the Astronomer was at fault, and the 
skeptic had in some sense the advantage. But at 
length a better series of observations are at hand. 
In certain examinations of the fixed stars it is found 
that these little points of light, when critically ex- 
aminod, appear to be moving according to a certain 
law and describing a minute orbit. The cause of 
this was perplexing to the Astronomer, and baf- 
fled all the efforts of one of the strongest minds that 
ever gave its powers to this subject. But finally 
the explanation was discovered in the fact that it 
was owing to the effect produced by the aberration 
of light — that as the Earth swept round its own or- 
bit, the light in coming to us caused the body to 
appear in different positions from that in which it 
then occupied. Let me make this intelligible. Sup- 
pose you desire to cross a river, and the stream will 
carry you down, and you wish to land at a point 
fixed upon on the opposite shore. Will you start 
out from an exactly opposite peint and row' directly 
across to the opposite shore ? By no means, be- 
cause you know you will in that case land below. 
Now how far above will you make your starting 
point ? Just as far above as the current will carry 
you down in the time you expect to occupy in 
crossing. But whathasthis to do with the velocity 
of light? I will tell you. Every particle of light 
that leaves yonder orb, in coming toward us 
sweeps downward in the direction of a right line, 
and when the Astronomer turns his telescope to 



20 



Prof. Mitchell's Lectures. 



receive that point of light and to cause it to pass 
down the axis of the tube, he must take into ac 
count the fact that he himself is moving with a cer- 
tain velocity. As he is borne on by the movement 
of the Earth, he must take in the other fact that 
every particle of light is comiog with a certain ve 
locity, and he must incline bis instrument so as to 
cause it to pass down its axis. The amount or 
inclination depends upon the velocity of light, as the 
distance you would be carried down the river de- 
pends upon the velocity of the water, and when 
we have inclined our tube so that the visual ray 
shall hit the mark, that inclination is precisely 
what ought to be given to it. Upon all this calcu- 
lation it is found that light travels twelve million 
miles in a minute. Here is confirmation strong and 
irresistable. 

But one step farther : It is found that certain 
stars are united together — not a planet revolving 
round a sun, but two mighty suns revolving about 
each other. To this matter I will call your atten- 
tion more particularly hereafter. In a certain Sys- 
tem of Double Stars which had engaged the scru- 
tiny of the very ablest minds, there were found 
discrepancies between the observations and com- 
putations which could not be reconciled for a long 
time. The problem seemed utterly beyond our 
reach ; bat at last, within a short time, one of the 
German Astronomers discovered that the whole 
difficulty has grown out of the fact that the veloc- 
ity of light was not taken into the account, and that 
the fact that the star was sweeping around a mighty 
orbit, and thus impressing its own motion upon the 
particles of light was not considered. When it 
was, all the discrepancies disappeared and the ve- 
locity of light comes out precisely as before. Here, 
then, are three demonstrations from different 



sources all coinciding ; I will not say exactly, but 
nearly so. 

The reason why I do not say exactly is this : A 
very short time ago I received a communication 
from M. Struve, a Russian Astronomer, who said 
he was engaged upon the subject of the Velocity 
of Light, andhad determined what is called the 
Constant Aberration of the Fixed Stars, and fuunrl 
the value for them was a little different from that 
obtained in regard to the satellites of Jupiter. — 
There was a slight variation, perhaps a thousandth 
part of the whole, yet it could be measured, and he 
said it was possible there might be a difference 
between the velocity of direct and reflected light. 
And he begs me in consequence of the peculiar 
position of my Observatory being more advantage- 
ous than his, to furnish a series of eclipses of the 
first satellite of Jupiter through the next ten years, 
with a view to determine thereby any difference 
between the actual velocity of direct and reflected 
light. 

This is the kind of accuracy attempted to be at- 
tained in our own day; and this, in truth, is the 
accuracy which is actually reached. You may 
think it is spending time in vain to work for ten 
long years to settle a question in which the discrep- 
ancy gives youonly a second decimal place ; but 
how important it is to know whether this mysteri- 
ous element in the original movement of light is 
different from that when it impinges upon the sur- 
face reflecting it, will be perceived when we reflect 
that the computation affects the movements of all 
these bodies, and that by a correct calculation o 
this apparently insignificant feature we attain to a 
degree of accuracy that we cannot reach in any 
other way. 



L 



LECTURE V. 



The Planet Saturn— Most diitant known to tlie Ancients— Gallileo's partial Discovery of its Rid gs— Discovery of its 
Satellites— Dimensions of the Rings— How were they First Placed There, and What are They ?— Their Solidity 
proved by Occultation of Sta T s, and their Shadows 'on the Planet — How their Position? are Maintained Ex- 



upon oui bys 

Attempt to Resolve them Discovery of Georaium Sidus— Of the Satellites of th^t Planet-Their Extraor- 
dinary Positions and Movements— But Three of them ever seen— Computation of the Orbit of Herschel— Per- 
turbations Observed— Leverrier— His Singular Position— His Piediction of the Time of Mercury's Tracst— He 
Attempts a Solution of the Perturbations of Uranus— His Calculations— Their Doubtful Reception— Their Tri- 
umphant Success in the Discovers of a New Planet— Adams's Simultaneous Computations— The Planet found 
to Disagree with the Calculations— Walkers Computation of its Orbit— Scrutiny of La Lacde's Catalogue of 
Stars— The Planet of Fact not the Planet of Theory— Its Mass Approximated by Discovery of a Satellite- Failure 
of Leverrier and Adams— Their Problem not the Problem of Nature— Supposition of a Group of Planets of 
which Leverrier's is One— Fame due to Leverrier and Ada^s. 



Ladies and Gentlemen : If it were possible 
for me to transport you to-night to the distance of 
ninety millions of miles in a direction passing 
through the Sun's annual track, and could there lo- 
cate you, your sight would in a short time be greet- 
ed with a most wonderful and sublime exhibition. 
You would see approaching you a magnificent 
"World, rapidly whirling upon its own axis. Around 
this vast central orb you would find a number of 
beautiful rings of light: these, too, would be seen 
to be whirling around with surprising velocity. On 
the outside of this again you would mark, as the 
object approached nearer and nearer, no less than 
seven subordinate worlds sweeping around the 
great central orb and with it rolling through Space. 
This is the Planet Saturn with its rings and moons ; 
and it is to this object I propose, primarily, to call 
. your attention to-night. It is the most distant of 
all the old planets known to the Ancients, its period 
is the longest, and its movement the slowest and 



most majestic. Up to the time of the discovery of 
the telescope, the wonderful characteristics which 
mark this object were unknown, but when Gallileo 
directed bis space-annihilating tube to its investi- 
gation he announced to the world that be found Sa- 
turn to be triple — that there were what be con- 
ceived to be two globes attached to the main body, 
one on the right and the other on the left. But 
these were oaly the projections of those mighty 
rings standing oblique to the line of vision, and 
seen imperfectly through his glass which magnified 
but twenty or thirty times. They appeared to him 
to be projections or globes attached to opposite 
sides of the main body of the planet. As the tele- 
scope was improved, these projections had their 
true character revealed, and it was seen that a flat 
annulus. or ring, passed entirely around the globe 
of the planet aud was separated by a certain 
amount of distance. As the power of the telescope 
was increased, and more minute investigations 



Astronomy. 



21 



(were made, it was found that the broad ring was 
divided into two rings ; and in modern times, with- 
in the last few years, by the aid of the mighty tele- 
scopesnow engaged in astronomical investigations, 
it has been ascertained that the outer of these 
rings is again divided, and there are no less than 
three which encircle the planet. The satellites 
were not discovered till long after the time of Gal- 
lileo. In the year 1655. we learn, one of them was 
seen ; and shortly after four more were announced. 
Then Sir Wm. Herschel, with his forty feet reflec- 
tor, detects the two minute bodies that seem to 
cling closely to the edge of the ring and are scarcely 
ever visible in consequence of the intense light 
thrown out by the Planet. Here, then, we have 
three rings and seven satellites, or moons, which 
belong to this most wonderful sphere : and remem- 
, ber that all these are sweeping with the planet 
] through Space, and as it wheels its circle about the 
I Sun, they move regularly with it, obedient entirely 
■ to its control. But what are these mighty rings 1 
The exterior diameter of the outer one is no less 
' than 177,800 miles, their breadth, measured entire- 
ly across both rings, is 30,000 miles, and their thick- 
ness is one hundred miles. How strangely are they 
constituted ! how wonderfully are they poised in 
Space ! We can understand the original move- 
ment of all the Planets with the exception of Sa- 
turn ; we can form some idea how this Earth, which 
we know to be globular, might have been projected 
by the Hand of Omnipotence, and caused to revolve 
in its orbit about the Sun ; but how was it that 
these stupendous rings were hurled in such a man- 
ner as to acquire that stability of movement which 
holds them steady to the action of the central plan- 
et, and at the same time rolls them onward through 
Space with the immense velocity with which they 
move ? This portion of our System baffles all con 
jecture; it rises entirely above the comprehension 
of the human mind. While we make some rough 
approximation to the notion as to how the other 
planets might have been launched in Space, we 
can form no conception of the manner in which this 
one was started in its career. 

But what are these mighty rings ? Are they 
merely a mass of light? Are they projections of 
the atmosphere belonging to the planet ? Are they 
portions flung out by the centrifugal force, and 
thus in some sense held steady in their position? — 
Are they solid bodies ? I answer ; They are solid 
bodies, and of the same material that composes 
the body of the planet. 

But how do we know this ? In the first place, 
we know them to be solid because, as the planet 
with its rings passes between us and distant groups 
of stars, such stars are first occulted by these rings. 
In the next place, they are not transparent in any 
degree, because of the fact that at the distance of 
nine hundred millions of miles we are able to mark 
the space of the shadows cast by these rings on the 
body of the planet. Night after night, month after 
month, and now almost year after year, have I 
watched with my own eyes the phases of these 
wonderful shadows. They are deep and dark, 
much blacker than any shadow you find cast upon 
the surface of the Earth. 

But again, they are able to exhibit the same 
characteristics themselves, and in certain positions 
we find the light of the Sun falling upon the body 
of the planet, which casts a shadow upon the 
broad surface of these rings ; and though we have 
the same blackness as before, here is the distinct 
shadow cast by the Planet upon the ring. Now, 
as we watch Them attentively, we find invariably 
that these shadows depend upon the position of the 
Sun and certain positions of the planet and rings. 
Just as the shadows which are cast upon the sur- 



face of the Earth depend upon the position of the 
source of light, so do these; and they follow with 
the same precision and accuracy the movement of 
the source of light that shadows do upon the Earth, 
and hence we cannot be deceived. 

The space by which the interior ring is separa- 
ted from the body of the planet is no less than 
twenty thousand miles, and the breadth of the ring 
is about ten thousand miles before we reach that 
space which separates it from the next ring, and 
so onward till we pass the outer one, of which I 
have just spoken. 

Now how is it that these rings are held stable ? 
How is it that they, detached from the body of the 
planet, are carried with that planet through Space? 
The stability of the rings of Saturn is perhaps one 
of the most difficult and perplexing problems for 
the Astronomer, and I would do injustice to the 
subject were I to pass over it without attempting 
to give some notion of this singular problem. And 
before I begin, permit me to explain the fact that 
there are three different kinds of equilibrium — for 
in the understanding of this will be involved the 
understanding of the explanation which I am about 
to make. I will attempt to exhibit these three dif- 
ferent kinds of equilibrium by the simplest possi- 
ble explanation. If I were to suspend a rod from 
the top, and cause it to vibrate as a pendulum, it 
would finally stop of itself. Here is an Equilibri- 
um of Stability. Why? Because if I move it ever 
so little to the right or left it will come back to its 
original position. Now if I take the same rod and 
balance it horizontally across my finger, it being 
equal in magnitude and density throughout, I have 
an E quilibrium of Inertia, because if I move it 
slightly it will not return, but remain wherever I 
place it. Now there is a third kind, exemplified by 
taking the same rod and poising it upon my finger : 
so long as I can hold the center of gravity above 
the point of support, I hold it steady; but the 
slightest inclination to either side destroys the 
stability. This is an Equilibrium of Instability, in 
consequence of the fact that every deviation tends 
td increase itself, and therefore destroy the equi- 
librium entirely. 

Having explained the three kinds of equilibrium, 
let us now, if you please, pass to the examination 
of the system of rings of Saturn. It is found by 
close investigation that in case these rings are pre- 
cisely circular, in case they are equal in density 
throughout, in case their center of gravity is their 
center of figure, and in case we add to this the fact 
that this center shall coincide with the center of the 
planet, about which they are placed, then the equi- 
librium is one of instability, and with the slightest 
cause that comes in to derange the system such 
derangement will go on increasing itself, and the 
center of gravity of the ring will commence moving 
in a spiral line about the central planet, the ring 
approaching closer and closer to that body till final- 
ly it is precipitated upon the planet and the whole 
structure is destroyed. On our examination of the 
ring we find it to be circular, and in the early ex- 
amination it was believed that the center of gravi- 
ty was coincident with the center of the figure of 
the ring, and moreover, that the center of gravity 
of the figure coincided with the center of the planet. 
This being supposed to be the fact, it seemed im- 
possible that this system should be perpetual, in 
case there was found in the satellites which revolve 
upon the exterior a disturbing influence sufficient 
to draw this center slightly away, and thus begin 
that very kind of motion which must end in final 
destruction. It was not till after La Place gave his 
mighty intellect to the solution of this problem that 
the truth was discovered. He found that the sta- 
bility could not be guaranteed in any other way 



22 



Prof. MitclieWs Lectures. 



than by making the ring unequally thick in differ- 
uts, or at least of a different specific gravity. 
This was not all: it was necessary to move the 
center of gravity from the center of gravity of the 
planet, and cause it to revolve about that center in 
a minute orbit. Yet. however strange this might 
appear, it seemed as if Satnrn was too remote for 
the telescope ever to verify the principle of this 
extraordinary statement. But it happens, fortu- 
nately for us, that in the position which we occupy 
in the system, these rings which are so very thin, 
are occupying a position such that the eye is sit- 
uated in the plane of the ring and we see them 
edgewise; aod when we view them in the first 
place they exhibit the appearance of a line of light 
drawn across the diameter of the plane passing 
through this center. Now in the disappearance of 
the ring by its taking up this position, we are ena- 
bled to examine with the utmost possible accuracy, 
and it has been found that the two extremity :: 
not disappear at the same time, and that there are 
inequalities upon their surface which are well 
marked and defined — the very thing precisely that 
La Place predicted would be the case, provided an 
instrument should be found of sufficient power to 
discover them to the eye. 

Bat this was not all: The most delicate micro- 
metrical apparatuses were constructed, and with 
these — which were capable of measuring the most 
minute distances — the spaces between the planet 
and the ring, upon the right and left, were deter- 
mined; audit was discovered that these spaces 
were unequal, not only unequal but variable, and 
not only variable but changing according to a cer- 
tain law. Thus it was shown conclusively and 
absolutely that the center of the planet did not 
occupy the center of the ring, thus bringing in the 
other condition requisite for stability, and fastening 
the whole system permanently in Space. 

Now bow could these rings have been formed 1 
Is it possible that they were attached to the planet 
after it commenced its journey in Space 1 It seems 
impossible for us to conceive how this might be 
accomplished; hence Borne philosophers have 
adopted the idea that they were formed at the same 
time with the Planet, and by the action 
same law ; and in all probability the celebrated Neb- 
ular Theory of the formation of the Universe de- 
rived more support from the exhibition of Saturn's 
system, than from all other causes combined. It 
was supposed that in the beginning of all things, the 
matter which now forms the Sun and planets and 
satellites, was diffused throughout all Space, or if 
not throughout all Space at least to a vast distance 
from the place which the Sun now occupies ; and 
that this incohate matter was divided and its parti- 
cle* held asunder by the repulsive power belong- 
ing to it. La Place conceives that in procesB of 
time — under the action of Gravity — the mass of 
particles commence a movement toward a center, 
and in coming from positions diametrically opposite 
they pass each other, and thus a -otation is com- 
menced about an axis. When millions of years 
shall have rolled away, and when this mighty sea 
of crude matter shall have been Elowly impreg- 
nated with gravity and consequently with motion, 
it will contract, and as it contracts its velocity of 
rotation must i till finally the cen*: 

force generated at the equator of the re*" 
mass overcomes the force of gravity, and a flat 
portion is detached from it in the form of a ring. 
"When this has been once loosened and detached, 
after millions of years shall have rolled round, we 
find the central mass contracting and leaving this 
ring in Space; revolving with the velocity due to 
the revolving mass at the time it was detached. 
Now then, in the process of the formation of the 



planet, this ring may by possibility break up and 
: i rsce into one mass. The same sc which- 

operated in the outset to detach the ring from IJhe 
mans, will in the second instance detach from its 
equator other masses which may form satellites;. 
ortheiT nihility may even remain and be- 

come solid in the form in which they were 
thrown off. If we admit this wonderful 
theory we can understand how it was that 

::_s system of Saturn existed, and how die 
conditions of stability were such as they now are, 
and how it is that this body moves on, century after 
century, without any change — — Eh the r kbiKty 
which fastens every part of it forever permanent. 

I do not pretend that this is the manner in which 
item 'was formed ; I do not know^I cannot 
fathom — any such mysterious problem ; hat one 
thing, however. I do know, and that is this : That 
if by the application of the higher powers of analy- 
sis this most extraordinary theory is demonstrated 
to be true, it carries the mind higher and nearer to 
the great Source of all things than any other which 
the human intellect has ever device- It gi e- 
more comprehensive idea of the omniscience and 
omnipotence of God than any other theory of -which 
I have any conception : for here, with matter in a 
chaotic form and scattered throughout all Space, 
having been brought into existence by the fiat of 
oil, by the action of one solitary law the Uni- 
verse — as boundless as Himself— is upheld and 
sustained forever ! 

"We pass on from the examination of this sub- 
ject to another. If in the Planet Saturn it seems 
as if t- -^rhich the system is r : ~ e n. e-5 

has been broken, we shall find in the i^: : ne: 
which revolves upon the exterior of this, a 
more strange anomaly. For a long time these 
were certain difficulties with regard to the move- 
ments of Saturn, which seemed to perplex philoso- 
phers : It b g out of its computed place, 
and the most extraordinary difference was seen in 
the movements of Jupiter when compared with 
those of Saturn. It was found that during the whole 
of the Seventeenth Century one of these planets 
was perpetually getting behind its computed place, 
while the other was getting in It • eemed 
that the twc moving in some way in which 
one was dependent upon the other. : 
to impossible to discover how it was to be made 
out. Finally the problem was taken up by La 
Place, and Bolvec and the explanation is perhaps 
as curious as any which has ever been presented 
for the examination of the human mind. Who 
would suppose that the stability :: :::- r-i_ im- 
pends in any degree upon the relation existing be- 
tween the periodic time of the planets I Yet this 

V t nd t incase the periodic times of any tw : 
planets should happen to be in such a relation to 

each other, that one of them taken a certain num- 
ber of times should be equal to the other taken 
a certain number of times different from the first, 
then irregularities would be introduced in the Bye- 
tern, which would go on always increasing in the 
same direction and the equilibrium would be that 
of instability. Now it happens in the periodic 
times of Jupiter and Saturn there is a close prox- 
:o such a relation, — five periods of Jupiter 
being about sixty years, and two periods of Saturn 
about the same time. Nowsupp:; 
piter and Saturn occupy a given position with ref- 
erence to the Sun, and they start out on their ca- 
reer: at the end of sixty years they will come 
round again to occupy almost exactly the same re- 
lative position; and whatever effect Ji 
have had to hasten the movement of Saturn, or 
Saturn to retard that of Jupiter, will again be re- 



Astronomy. 



23 



peated in the same way and in the same position, 
without the possibility of restoration, except with 
a difference of configuration on the opposite side. 
Strange as it may appear, this particular case 
comes very nearly, though not quite exactly, to 
that of these planets : they do not reach the same 
position by an amount equal to something like six 
Or seven out of the 360 degrees : here they are a 
little behind at the succeeding year — at the next 
Still farther — at the next they have changed yet 
again, till now after about 2,500 years they come 
to occupy the first position in all the successive 
rounds of their orbits; and not till they have gone 
entirely around will the compensation be effected 
and the System be restored to its original condi- 
tion. Such is what is called the Long Equation of 
Jupiter and Saturn. 

I do not mean to say the period is 2,500 years ; 
because in consequence of the fact that they come 
to resume the same relative places in different parts 
of their orbits the same will be effected in a shorter 
time: and indeed in consequence of this difference 
of configuration in different parts of their orbits it 
is accomplished in nine hundred years. 

It appears then, that this particular case which 
seemed to set the law of gravitation at defiance, 
is reduced absolutely within the control of the law, 
and a most beautiful explanation of the phenomena 
is presented. 

When* these difficulties had been removed, a 
more rigid scrutiny seemed to reveal others in Sa- 
turn, till finally, after having exhausted all the 
means within the limits of the Solar System to ac- 
count for them, some mind ventured to pass the 
limits that had hitherto circumscribed it, and say, 
•' There must be a planet upon the outside." But 
no one dared at that time to undertake the resolu- 
tion of the vast problem, by whose solution the 
position of the unknown body could be deter- 
mined. Fortunately for the world, in 1781 Sir 
Wm. Herschel in one of his telescopic explora- 
tions found an object which attracted his attention : 
In short, he saw in it something which resembled a 
planetary disc. On the following night the exam- 
ination showed that body to have changed its place ; 
yet so little did he expect to find another planet, 
that he announced he had found a comet and com- 
menced to compute its orbit; but found no elongated 
orbit would suit the place which had been given to 
it and that nothing but the circular, or nearly so, 
would fulfil its conditions. It was found to be a 
planet revolving outside of Saturn, at a distance of 
eighteen hundred millions of miles from the Sun. 
This (first called Greorgium Sidus in honor of King 
George III.) is known by the name of Herschel — 
more generally called Uranus. 

In the course of five or six years, Herschel an- 
nounced he had found six satellites revolving about 
the body ; but what astonished every one, v/as the 
announcement that these satellites, instead of jful- 
lowing the analogy of the other known planets by 
revolving in the same direction in which the plan- 
ets moved, were actually moving backward in their 
orbits, and nearly perpendicular to the plane of the 
ecliptic. Here was a difficulty in the great Sys- 
tem of the Universe called " La Place's Theory," 
which I have already announced. If this System 
was formed as he supposed, how is it possible to 
account for the retrograde motion of these satel- 
lites, and for the fact that their planes are nearly 
perpendicular to the plane of the ecliptic? Per- 
haps it is impossible to account for it ; but if we 
will admit that such a thing may occur as the im- 
pinging of a comet upon any body in our System, it 
would not be impossible to account for those retro- 
grade movements, nor for this great inclination, by 
supposing at the time this was a fluid mass, the 



movement may have changed its rotation upon its 
axis, and have caused the satellites to take the po- 
sition they now occupy, i do not present this for 
any one to receive as a true hypothesis; it only 
shows that those who adhere to a particular theory 
will rind ways and means of explaining difficulties 
which others never would think of. Neither do I 
wish to be understood as having adopted Laplace's 
theory ; very far from it. It remains to be demon- 
strated yet, and it is possible the means may yet 
be attained whereby, by the power of analysis, we 
may bring out the truth or falsehood of this most 
stupendous theory. We are obliged, therefore, to 
accept the statement of Herschel for the present, 
although, so far as I know, up to the present time 
no eye has ever seen more than three out of the six 
satellites which be tells us revolve about this planet. 

When this planet had been watched a suffi- 
cient number of years, and the observations had 
been made by means of which its orbit could be 
computed with accuracy, and the place which it 
had occupied years and years before its discovery, 
on running back through the Catalogues of Stars 
which had beenformed by preceding Astronomers, it 
was found that this body had been seen a number 
of times and had had its place fixed in the heav- 
ens, being regarded as a fixed star. These early 
observations were of infinite value in determining 
a more accurate orbit of this planet, so that long 
before the elements of this orbit were known it 
was possible to predict its position in all coming 
time. But when these predictions were made, 
and when observation and theory were compared, 
it was found that the planet was deviating from its 
computed place — it was found that no analysis 
could confine it : it has broken away from its com- 
puted orbit, and at the distance of eighteen hun- 
dred millions of miles from the center this body 
seemed to be moving lawlessly through the heavens. 

In order to resolve this great problem, it would be 
necessary to go into a minute investigation of all 
the observations that had been made; to go back 
from the planet through the whole Solar System to 
the Sun itself, and to ascertain with the most perfect 
precision what influence was exerted by all the 
known bodies upon this one. If, after every possible 
influence had been admitted, accounted for and ap- 
plied, there were yet outstanding inequalities re- 
maining unaccounted for, it certainly became 
necessary to look for their cause beyond the 
limits of the known Solar System. This was the 
problem taken up by Leverrier, and to which I will 
now call your attention. 

Perhaps there is no person living in the world 
who occupies so unfortunate a position as the indi- 
vidual just named. This may sound strangely in 
your ears. The difficulty is this: That he has ac- 
complished the resolution of one of the most sublime 
problems ever attacked by the human mind — lite- 
rally and truly accomplished it — and yet that prob- 
lem turns out not to be the problem of Nature, or 
ofee that God had given to be resolved ! I know how 
difficult a task it wiil be to explain this, and it is 
this particular difficulty which constitutes the truth 
of what I have stated, that his position is one least 
to be envied ; for he probably never will receive the 
credit due to him. in consequence of the fact that 
the planet so recently found is not the planet of 
his analysis. 

But now for the examination of this matter. — 
Leverrier is a comparatively young man, and had 
shown the power of his genius by a rigid examina- 
tion of the conditions involved in the movements of 
the Planet Mercury. He had taken up the old ta- 
bles which seemed to govern the movements of this 
Planet, and bad corrected them from beginning to 
end. It was believed that the knowledge which 



i4 



Prof. jL':',c":s Lectures. 



we already had of the movements of fids body was 

szrrE:er:-7 : ::e:: :";: til rra;:l: al : n-y :se 5 E.e 
tra._5 .: :::::." yla.ze: =:::■« :r.e 5 _r wz'E ;;■- 
curred nos long since, gave the opportunity of test- 
in r :l.e - : :z:a:7 :: _:;- :~ - E~ es v.: zr; ■_: :r:.:e 
z:;: ::::.: i:.:e: : a.ri w:;i:;r rer;:? ;:::: 
In :::nr"f.7 yz z::er :: :b e vr. .•". ; ari ~ r re :- r. 
centrated at Paris, and presented for examination, 
it was found that he had predicted the instant at 
which the Planet should touch the disk of the Son 
rzrre E.::z:z:e'.y :::: £.ry :Eer :::;::-;: rzi 
attempted it ; and indeed he only tailed by the 
amount of sixteen seconds of time. 

E.s zy:ez: sn::e;> ir: :Es z zz-ri:Ez? ir zz:ec bis 
frier z --..:■ a zy: m reryzes: l\izz :•: arrezzz: tire resz'.z;- 
tion of the problem of the perturbations of Uranus. 
He commences, not to stdm superficially over the 
surface — taking for granted what had already been 
done — but goes back to the first observation record- 
ei azzr:z:esca;zzzi e~e:y :ze 1 :~z :ze srreazz 
of time, sifting out everything which belongs to 
ez:z :ne ::" :.rfem. >E: ■;::.>:;: ~::'z :Es. be ;:z_- 
mences a review of all the planets that can ope- 
ra:e zy :z ::s rr; : : :z. maze; a ltT :ze;-y :":: Sa- 
turn, and for Jupiter, takes into consideration even 
the change of position occasioned by the action of 
Jr:::e: r: :z Szrzzrr ::senl szzi :ze rzizr:e sz: se- 
quent changes in the action of Saturn upon the 
planet nine hundred millions of miles distant from 
it- All these things are gone through, and with the 
hand of a master he holds the problem steadily be- 
fzre bis zyszre. ani seizes e~er;' r :.r: w::z periec: 
cer:3.;rrr. A: '.;:::; re la; a:: :zr :e: ::: :_e :;:■ 
turbation due to the action of any known body in 
the Solar System, and there is a certain amount 
yet outstanding. And now the grand object is to 
pass upon the true elements and see whether it be 
possible so to locate a planet in Space that it may 
account for this outstanding perturbation, and 
whether by giving . to it this position it be possible 
to find it How did he attempt this? Tomostper- 
s:r« :: wmli seerz r::e:".y : eyzzi Ee z:zs: ::" :ze 
hzzraz in Telle::. 3_: "e: rs ::z5.zer. 

In the first place : Bode's law of distances told 
Mm about where it would be located in Space. As 
Sarrrr — -.» a; :z: :"*Ee as iar :::rz :ze 5zz, as Er- 
pirer. zr i 7:_rzs : ; - 

right to conclude that possibly the unknown body 
vEzE b e 1:: = : i :- ". : - :. - 
Sun of Uranus, or three thousand .six hundred mil- 
LEns ::"-_r..e- ; Ezv.rz; :;:z::.ei:ze *:s:zz:e Eer- 
ie: 5 ".;.— zr-'e ':.'.. :i :.:.e ~y e:i: r: .v.: ; -. :::e~r. :••::■ 
ty be:zrne r::xirzi:eE zz:-*r;, 3 ;: zc~- ::e r:ez: 
p':iz: •s-s.s :': ze: :re y a:rl:Ez- r :»:::: r. ar. i i: :ra: 
coEi : e E:zE: i :.e'::r.: :.'l:~*r ::s y ::^ re- 



ar.! far: re: a ■■" 17 1. : 



e : -er. nzre. 
^rriiar :r ::' 
Ee ::zrz 
::,- :"a::be: 
idius. or di- 
7z:s be 



3/;-: ::-::rr;-:lr -r.rr.:v:-r b ■■ -7 be 'mrE All 
he had to do was to find where Uranus was drawn 
farthest from the Sun, and looking out in that di- 
rection he locates the body that draws it out. Hav- 
ing, :r_erefbre, found one position, and the time 
when Uranus occupied that position, from its known 
periodic time he traces np its movement and says 
'--'■ 5 "- : £. -jl" -" ^'--- ::::y7 sr:r a r: ; rr ir :iie 
heavens. He reaches the conclusion of his inves- 
tigation and presents the results to the Institute at 
Paris; they are thrown before the scientific world; 
they are received with incredulity and doubt by 
:r e res: J.~:r.§ A; v: :r :rre-£ : :rer::';lrrrseer:5:"j 
have been too migbry — too intricate for any mind. 
But Leverrier desires them to point their telescopes 
to the position in which he says the unknown body 
exists : his requestis granted.' and lo ! to the amaze- 
ment of the whole world, there is a planet exactly 
in the place pointed out, (Applause ) 

There was the triumph complete ; and if any had 
: e ::e : ;\: ::ei :b:=e :;rl:s -^ere r : tt rerr';Te;. 
ari :re -s-'rile vr;r 1 ra:£ vrirb ;re r:aise> 0: the 
great Astronomer, Leverrier. 

And now, as if to make everything doubly sure, 
it is found that a young man of England had been 
engaged in investigating the same problem, bad 
re^:r.er :re sarre :rsrl:= ari sever rr:r:.;s :e!:re 
Leverrier had published his, he had presented them 
:: :re A = :::_; r_e~ E. 7 a. : 1 /is : ~r. Err : :rr ard 
the Professors of bis own University. They, not 
daring to take the responsibility of uttering them 
before the world, failed to do it ; but so soon as 
Leverrier S computations were known, so soon as 
the planet was found, then it became certain that 
be had been investigating precisely the same prob- 
lem and reached the same identical results— each 
confirming the other, and the two combined con- 
vinced the world that they had reached the true 
results. (Applause.) 

Now do you think it possible that this is all false? 
Having carried you to this point, am I obliged to 
:e .. 7 : r : r r : : r 5 r : rr . .. : a-; : . 5 1. a .: _ . . r — .; a : - 
ever to do with finding of that planet? Tet I am 
absolutely obliged to do it, for it is true. How then 
shall I show you and convince you, that in announc- 
ing this truth I do not pluck a solitary laurel from 
the brow of this great man. No, not one ! There 
they are, green as in the moment of their winning; 
and there they must remain forever. (Applause-) 

As soon as it was known that the planet was dis- 
covered, telescopes were directed from every part 
of the world to its scrutiny. Its movements were 
followed with the most intense anxiety for the pur- 
: ir :: £.s:e:;a:_ r r r:^v zea:y :re ; " ::;r: : rei 
with the computed elements. Adams led the way, 
as he had before done in the computation of the 
elements derived from theory .and when he reached 
to the knowledge of the actual distance of the dis- 
covered planet, he was the first who found and an- 
nounced that hitherto the discrepancy between the 
distance now absolutely known, and the first com- 
putation of the distance, amounted to about three 
times the distance of the Earth from the Sun. He 
aar :; rr: :y : rrr r:ar.:-r. :e - Ee :re : s:;- err :7 a: 
at the time of the discovery it ought to be thirty- 
:r re e timet the instance nf the Earth from the Sun 
whereas it was but thirty times. This did not ap- 
pear to be a very great discrepancy, yet it was 
rr :: e :r ar v- as ar : ::y- are : : :':: r.s-i i: rerare:r:r 
of three times the distance of the Earth on the op- 
posite side, there would have been more reason in 
it. because it would have coincided more nearly 
with the distance revealed by the law of Bode. It 
b e err ed,in consequence of the fact that it had fallen 
:r. :re Esiie. ir, i.rre se_:r ;; irare v.;..a:ei :_: 



lot again: More time 



ari ; e::e: obser- 



Astronomy. 



25 



vations are obtained. Finally, there seemed to be 
no data to commence a computation of the orbit, 
that should reveal what the phases of the Planet 
were in years past and gone, as well as what they 
will be when hundreds of years shall have rolled 
round. One of our own countrymen engaged in 
this investigation with ardor, zeal and success. — 
Walker, of the United States Coast Survey, ob- 
tained an orbit, and thought he could trace the mo- 
tion of the planet backward for a hundred years. 
In tracing it backward he hoped to find in the cata- 
logue of the Fixed Stars some one that might have 
been observed which should prove to be the planet, 
and thus give us the advantage of a long series of 
observations extending over many years. The 
later catalogues were examined: he went back 
fifty years, till finally he took up the catalogue of 
Le Lande, made in Paris. He found the Stars re- 
corded by him, computed the reach through which 
he knew the pianet to have followed at that date, 
til! he discovered that on the 10th of May, 1795, Le 
Lande had observed a star which then occupied a 
place where he computed the new planet should 
have followed at that date. But how could he veri- 
fy his prediction that this was the place, and Le 
Lande had seen the planet at that very date ? He 
turns his telescope to the region in the heavens 
which Le Lande's star had filled, and if it were a 
fixed star it would be found there, but if it should 
turn out to be a planet, then would that spot be 
blank. The telescope was directed and lo! the 
spot was a blank. Thus it was believed that this 
was the place of the planet; but when this place 
was taken into account, and when this observation 
was combined with later ones, behold ! the orbit 
determined for this new body, and the periodic time, 
fell entirely beyond the limits of Leverrier's and 
Adams's computations, who had announced that it 
could not be a period shorter than 210 years nor 
longer than 268 years. Here was a great discrep- 
ancy, so that it was impossible that this could be 
the planet of their theory, in case these observa- 
tions could be sustained. And now it was that every 
eye was at once directed to the catalogue of Le 
Lande, to see what his observations were, and dis- 
tinguish as to what observations were marked 
doubtful. There were discovered two little dots 
placed opposite this observation, and referring to 
his preface, it was found that observations marked 
with dots were not to be relied upon. Those who 
longed to find the grand theory which had been 
built by Leverrier to be true, hoped in this mark to 
find that which would save the system. So soon 
as a knowledge of this fact came to the Institute at 
Paris, they appointed an Astronomer to review all 
the old manuscripts of Le Lande. It is found that 
on the night of the 16th of May, 1795, he made this 
observation and marked it doubtful. On the same 
identical piece of paper is discovered an observa- 
tion made on the 8th of May, on a star, which he 
believes to have been incorrectly made ; this he 
rejects and takes up what he thinks to be the same 
star, observes it on the 10th, prints that observation, 
rejects the other and marks the printed one doubt- 
ful. Now what a singular state of affairs is here ? 
But the moment the orbit of the planet is comput- 
ed, that star of the 8th, is found to be in the place 
of our planet; and so instead of having one we 
have two observations, and the distance between 
the two stars of the 8th and 10th is the same the 
planet ought to have traveled, upon the hypothesis 
we have already given. 

Now there seems to be no doubt left in regard to 
the fact that Adams and Leverrier stand before the 
world in a different position from what they had 
previously occupied ; but there is something yet 
left to be ascertained. There is a planet found in 



a most wonderful manner, occupying almost pre- 
cisely the position their' planet did occupy. Is it 
the planet that accounts for the perturbations of 
Uranus, or is it not? This is the next question 
for examinaticn. In order to ascertain) that 
fact, it became necessary to know the mass of this 
new planet. In the onset it seemed hopeless to 
look for an answer to this question for a long period 
of years. But the scrutinizing gaze now directed 
to the heavens does not permit the most minute 
point to escape. At length it is announced that 
from the distance of three thousand millions of 
miles, the light of a little satellite is flung back all 
the way to the Earth, and that little satellite, by 
its periodic time around its planet, reveals to us 
how much matter belongs to this most distant orb. 
Now, although at present I do not know precisely 
the amount ascertained, for we have only approxi- 
mated to it, yet the knowledge we have obtained 
tells us most certainly and absolutely that no mass 
can be assigned consistent with the periodic time 
of this satellite, which will account for the pertur- 
bation of Uranus ; hence the conclusion is forced 
upon us that this is not the planet of theory, but 
we have got to look farther before we can settle 
the question as to what produces all the perturba- 
tions belonging to this interior planet. 

Now can I reconcile my statement or not? Have 
Leverrier and Adams failed in the problem they 
undertook to investigate 1 Have the facts I have 
brought out lowered them in your estimation ? I 
hope not ; for I can truly feel for these great men. 
They had resolved the problem they undertook; 
they had done it correctly; and m this they dis 
played the most extraordinary genius that ever has 
been exhibited by any human mind; but alas! for 
their fame, the problem they solved was not the 
problem of Nature. God has permitted us to see 
that, and if I were permitted to interpret anything 
I would almost say, here is a special Providence to 
reward the lofty and powerful efforts of mankind. 
Such was the structure of the System that it was 
impossible to attain to a knowledge of it without 
the solution of this problem, and such was the gran- 
deur of the problem solved, that it deserved as its 
reward a World, and a World was given. 

I know you can comprehend this if 1 bring you 
back a little, and refer to what I told you the other 
night with reference to the Asteroids, which sweep 
around between Mars and Jupiter. Suppose, be- 
fore these were discovered, some daring genius had 
undertaken to resolve the mysteries in which the 
movements of Mars were involved and should have 
reached the conclusion, that they were produced 
by the action of a certain planet located between 
Jupiter and Mars, at a certain distance, and revolv- 
ing in a certain period of time. Now here is a pro- 
blem presented for solution, and worked out with 
consummate skill; but when the facts come to be 
known this problem does not exist in Nature ; for 
there are no less than eight planets revolving in 
these limits, and combined they produce the same 
effect that would have been produced by the con- 
structive planet. This is precisely the case in 
point, and this is the reason why it was impossible 
for Adams or Leverrier to give the elements of the 
orbit of the planet now found; for I have no doubt 
this is only one of more bodies which exist in the 
same region. (Applause.) 

Whether we shall ever attain to a knowledge of 
them, or be permitted to feast our eyes on them, it 
is impossible to know ; but, a year ago, in the dis- 
cussion of this subject, when I did not doubt that 
this was the planet, I ventured to say that, in case 
it should be found hereafter that the orbit of this 
planet was not very eccentric — carrying it off to a 
much greater distance than it now is, and thus ac- 



26 



Prof. MitckdTs Lectures. 



countins for the fact that its distance is less than 
that assigned by the law of Bode — that it was one 
of a group, how extended it is impossible to say. 

I know the difficulties which I have had to en- 
counter tonight. I have tried to impress 
minds with one great Truth. I do net know "how 



successful I have been ; but I cannot rlose without 
repeating once again : Although this new planet 
is not the planet of Leverrier and Adams's theory 
yet it does not in the smallest degree detract from 
the jast fame which is due to them for the resolu- 
tion of this mighty problem. (Applause.) 



LECTURE VI. 

A Journey to the Stars — Its Difficulty.... The San 83 seen from Neptune— Intensify of its Linht. . ..New Unit of 

sure.... Parallax. ...View of a Son tilliDg Earth'i Orbit from the Fixed Stars. ...Attempt to Measure the 

Distance of the Fixed Stars — The Method employed— Instead of Par= .il; : te aberration of Lieht and Nutation 

of the Earth Discovered Hersch- ±u.i the Parallax of Double Stars— He fafs. but Discovers 

Sans Revolving about Saos Heliometer applied «o Measurements Discovery that Fi^ed Stars are Moving 

. . ..Observations on Double Star No. 61 Cypni — Its Para'.iax jptrerinined— Its Distance The Mi!kv Way Dis- 

tapce measured by the Eye— B- - lea :ope — EJerscbe.'s r.xplo-arlon of the Milky Way — Extent of the Milky 

Way— Immense Pow?r of Lord Eosbc 5 Telescope Movement of Oox System around a Mighty Orbit An Idea 

of Eternity — Of the Power and the Knowledge of the Creator. . ..The Cincinnati Observatoty— Pei3onal 
■fatten. „ :. 



Ladies axb Gzntlzmzn- : Had I been permitted 
to choose the circumstances under which I should 
deliver the Lecture of this evening. I would gladly 
have had the clouds that shut out the light of the 
stars removed for this one so.itary night aurine the 
Course: More especially would I have desired it 
tonight, in consequence of the fact that I wished 
to move outin imagination anion? those fixed stars, 
and, inasmuch as the journey is of itself sufficiently 
difficult, I could greatiy desire that there should 
be no obstruction in the way. Bat under all the 
circumstances, perhaps the subject itself will be 
sufficiently interesting: and trusting, therefore, to 
your attention, 1 will endeavor to make an explo- 
ration to-night which shall carry us to the utter- 
most limits yet attained by the human mind and 
eye. 

In the examination which I have thus far made, 
I have confined myself exclusively to our own So- 
lar System. I have announced the ereat laws by 
wh'ch it is governed ; I have attempted to explain 
the manner in which these laws operate upon the 
various bodies belonging to it, and to show you 
how worlds are moving through Space obedient to 
those laws and yet subjected to the influence of 
each other. But we are to leave this System. 
grand as it is. and traverse through regions and 
over distances which we have not up to the pres- 
ent moment dared to conceive. I know how diffi- 
cult is the subject which I am about to approach, 
and I approach it with embarrassment. I know 
how difficult it is to comprehend these immense 
distances — these vast periods, and these mighty 
and innumerable objects, in such a manner as may 
be p-esented intelligibly to the mind. Still we 
shall venture upon the attempt. 

If it were possible to transfer you to the outer- 
most limits of our Solar System, and there, resting 
upon the body of the Planet Xeptune. we could 
look backward over the space we have tra ~ - 
we should find the Sun. which to us is so bri 
and so magnificent, already diminished so as n:>t 
to appear larger than does the planet Venus now 
appear to us on the E arth. But think not that this 
diminution in apparent size will diminish in like 
proportion the ligdt which the Sun throws out : for 
if there be inhabitants there, they wild receive more 
light from this diminished Son than could be thrown 
out by a handred of our Full Moons ; so it is still 
daylight to them. 

But if objects are diminished by accomplish- 
ing this journey through Space 3*000,000,000 of 
miles, what do we see when we attempt to cross 
that mighty gulf which still separates us from the 



' nearest fixed stars ? It is across thi3 almost illim- 
I itable space that I wish to carry you to-night. The 
j unit of measure with which we have gone through 
the examination of our System, has been the dis- 
tance of the Earth from the Sun — the radius of the 
Earth's orbit. In makin? our measurements to- 
we must adopt a different unic, for this is too 
small ; and we propose to take as one unit of 
| measure the distance to the nearest fixed stars. 
With that unit, if we can attain to the knowledge 
: of its value, we shall proceed to measure the Uni- 
verse by which we are surrounded. 

First, then, let us attempt to explain what is 
meant by Parallax ; for this term I shall employ 
frequently in the course of my remarks. The par- 
a'. ax of any body is the apparent change in the 
| place of that body, occasioned by a real change in 
; the position of the spectator. If I change my po- 
! sition in this room, occupying that of yonder indi- 
' vidua!, I find every other person apparently to have 
changed his place ; this is a parallactic change. 
As you have, while sitting in a railroad-car passing 
through the borders of a forest, fastened your eye 
upon an individual tree, and have seen the others 
apparently whirl rapidly around it. so is this appar- 
ent change in the position of the heavenly bodies. 
Now the question is this : Is it possible to deter- 
mine any ccange in the place of the fixed stars, 
occasioned by a change of the place whence they 
are seen ! If this can be done, measured, appre- 
: ciated and determined, then, knowing the disrance 
■ which separates the two points cf observation and 
the amount of change occasioned by the change of 
place of the spectator, we find, without difficulty, 
I the distance of the object. When the followers of 
j Copernicus announced that the Earth revolved 
| about the Sun in a mighty orbit 200,000.000 miles 
; in diameter : moreover, that the axis of the Earth 
upon which it revolves once in twenty four hours 
was ever parallel to itself; and still farther, that 
this axis prolonged to meet the celestial sphere, 
was the north pole of the heavens, the objector at 
once said. •• It is impossible : because, if the 
Earth's axis, being produced to meet the heavens, 
\ touches it in a particular point, this point carried 
parallel to itself around a mighty orbit of 200.000.000 
miles diameter, will cut in the heavens a figure 
having also the same diameter; and certainly this 
circle described in the heavens wi i be visible to 
the eye." But it is not visible to the eye. If the 
whole diameter of 200,000.000 miles were filled by 
a globe as brilliant as our San. at the distance of 
the fixed stars it would shrink absolutely into a 
point which no micrometer ever made by man 



Astronohty. 



27 



could measure. Here there was a sort of indic- 
ative knowledge with regard to the distance of the 
fixed stars. It must be so great that the whole 
Earth's orbit, viewed from them, would shrink 
into an invisible point. 

So soon as telescopes were perfected and the 
division of the circle obtained in the most accurate 
manner possible, by means of which the most deli- 
cate observations could be made, the human mind 
again returned to this grand problem and attempted 
to pass these hitherto seemingly impassable limits 
to measure the distance of the fixed stars. And 
now let me attempt to explain one of the methods 
adopted to accomplish this grand object. 

Suppose it were possible to erect in the center of 
this room a rocky pier, going down through the 
base upon the solid rock itself so as to be perfectly 
immovable. Now then upon this rocky pier let 
me adjust a telescope of the highest possible capa- 
city, and let the axis of that instrument be erected 
so as to have a direction exactly vertical. Having 
accomplished this, let me screw it to this rock, so 
that it shall never move, but be forever permanent. 
Now to determine the exact axis of this telescope 
and to make it appreciable, let me fix in the focus 
two most delicate lines of spider's web, which are 
so very fine that they may be regarded almost as 
invisible mathematical lines. Let them intersect 
each other in the axis of the telescope and their 
point of intersection upon looking upward, will give 
a precisely vertical direction. Now I have a piece 
of machinery prepared to make my examination of 
a few of the fixed stars, to determine whether 
there be any change from the fact that the Earth 
is sweeping round in its orbit. Place the eye to 
this tube, and watch till some particular star, that 
you may have selected and which lies exactly in a 
vertical direction, passing through the zenith shall 
reach precisely the central point of the telescope, 
so that the line of vision, like a prolonged axis, 
pierces the star exactly. Now we record the ob- 
f servation which is made at a particular hour, and 
when the Earth shall have rolled round its axis and 
brought it to the same point we observe it again, 
and so through the whole year. Now then if there 
be no change, that star will ever pass at the same 
moment exactly through the same point across the 
axis of the telescope. But suppose it should 
deviate a little from the point of iotersectioia, 
and at the end of the year it shall have described a 
minute orbit, the center of which is the central point 
where the axis of the telescope pierces the heav- 
ens: the magnitude of this little orbit, accurately 
determined, is the amount of apparent change oc- 
casioned by the revolution of the Earth in its orbit, 
and this would be the parallactic motion of the 
star. 

This method was adopted by one of the distin- 
' guished Astronomers who attempted the resolu 

tion of the problem of the distance of the fixed stars. 
He did not succeed : it defied his ingenuity ; still, 
he was rewarded in his efforts, if not by the attain- 
ment of the object to be accomplished, at least by 
others equally important. He found the star upon 
which he fixed his eye moving, not as be supposed 
it must move, in parallactic change. but taking a dif- 
ferent course. For a long time the cause seemed 
to be wrapped in impenetrable mystery; but 
he finally found it to be due to the fact that the 
Earth was moving with a certain amount of velo- 
city, and ligi t also was coming with a certa n ve- 
locity, and the two forces combined gave to that 
star an apparent motion which, when the cause 
was known, was perfectly explicable. He discov- 
ered in this way the Aberration of Light, and also 
a certain other change, shown by the fact that the 
Earth's axis is not precisely parallel to itself, but 



owing to the influence which the Sun and Moon 
exert upon the protuberent matter around the 
equator, it is made to vibrate, as it were, through 
a very minute arc in the Heavens. This is called 
Nutation : and these two great discoveries were 
made in the effort to resolve the problem measur- 
ing the distance of the fixed stars, 

I desire to trace up the history of this examina- 
tion, to show how Science has progressed, and how 
Art has been gaining one victory after another, 
even when it seemed to be impossible to make the 
slightest progress. I pass rapidly down to the se- 
cond great effort made to determine the parallax 
of the stars. 

Gallileo had even projected this plan, but never 
found himself in possession of instruments requisite 
to make the examination. The plan is simple and 
will be easily understood by all who hear me. la 
examining the heavens, we find among the fixed 
stars certain ones that appear single to the com- 
mon eye, but when examined with a powerful in- 
strument they are found to be composed of two," 
three, four, and sometimes as many as six, clus- 
tered together so closely that to the naked eye they 
appear as a single object. Now, after Herschel 
commenced bis review of the heavens, he found 
these clustered stars scattered profusely, and the 
idea occurred to him that the apparent near prox- 
imity of them was occasioned by the fact that one 
was sunk in Space far deeper than the other, and 
the visual ray passed near or exactly through the 
least distant one. In case this hypothesis might 
be received as true, these double stars, in which 
one of the objects was double the size, and in 
this sense appearing to be half the distance of the 
other, would famish a most admirable means of de- 
termining whether any parallactic change took 
place in consequence of the revolution of the Earth. 
Suppose I am so situated as to occult any object in 
this room by one of the colamns before me : by 
throwing my head slightly to the right the object 
hidden will appear to come out on that side; or, by 
throwing my head to the left the same object will 
appear to come out from the other side. Just so in 
these minute double stars. If the observer start 
from one extremity of the Earth's annual orbit, and 
find this minute star on the right hand side of the 
larger one; if he come round and continue his ob- 
servation till he reaches one-quarter of the whole 
circumference, when he finds it is hidden behind 
the larger star ; if he reach tne other extremity of 
the circuit, and find now the minute star is coming 
out on the opposite side ; if, moreover, this change 
occur every time the Earth makes its annual revo- 
lution, it will demonstrate most conclusively that 
these changes are parallactic, and occasioned by 
th^ fact that the observer is sweeping eround in 
the Earth's orbit, and viewing the objects from dif- 
ferent positions. 

Such is the nature of the investigation undertaken 
by Herschel, and there seemed to be every reason to 
believe he would be successful. But dia he suc- 
ceed 1 No. He found that these stars were mov- 
ing; and here again were his efforts rewarded by 
one of the most brilliant discoveries ever made. 
He fouud in these closely-united objects that there 
was a motion, but not of the kind he anticipated; 
he found that the one was moving about the other, 
and on a better view, that they were both revolv- 
ing about their common center of gravity. Is it 
possible that there distant orbs were energized by 
the same kind of influence which operates on the 
Earth's surface, and that this Law of Gravitation 
extending over this immeasurable gulf, seized these 
suns and held them obedient to its control, causing 
them to revolve about each other? 

The announcement that these motions were go- 



. i - m . •: '.- r Mr m 'm .. :. — t." : — ; Lr ,: :: ; 
~ - " ' ■ v . _ - 

: : " - _ . ■ 

- - 
■mite 

:nr _ I _ qj 1 7 : • - 

. - • 

7 - . \ _ . ' i 1 - - : ■ ■ - - _■ 

ZJZ- f . _ r_ .___- - . ; : r : - . - ; ; : -^' - :i - l - 
mm ■•„:- : -•'■:•;;; li : immmimmt r :t; ::-■■; 

- 
efior: : - : _ DragreHsrng. Aan- 1 

M/"~ : : r . '. m f . : i : - i z :_ m • ■ t ' - m. mariii: 
gnri measures mafle yea: l - 
; :m - . _ m . ■ t ._ m :___ 

_ - . - - - an r : ■ . - • 

. : ' t : 7 . - 1 •. ~~ -":--. 

7.. .".'i -; l: :.'-ie: l:m ~ m : mm. v: mmlm .: e.« - iu~ 

m - ' i- ' £ "-"..«!_• r r \ -:'-.: m r ■ m_ r .: v ml: m 

si ". ■ J! . . ; - : 

-i-nc is: - sil::l j. zia q:7 eif? m - m m : — ..: 

E . - " " t — t:-.'.r m: - : . i . - r : 

vmll : : :c: M ::: t : m -. ~ : :■-■■.; : r ::: ;iu : vm 
: ~ : - :_ ;r: i r: ; ; ; - i v - - - 

.. 
fiistEi T ' . . - : 

: : ' -" ~ : : i '.. utlii ye::~: : m 
3nk me to purr i : . 



" ~~ "- - : _'_ : " " . . . : 



: _ - _ m " - - - 

' ■ ~ - : r;.i ;:: - . _i _ : : - : 

- " -7 - - - - m" _ : mo-~~ 

iD~ik jvass tax tee i 

— - 
' -~ '■- - :•: i- r ! "L- rr.n:'r: ■' _ • i ; 
— - lmmm 7. ■ i m f - ■-■; - i :i - -•_ - ; : : --• m>t iMf 

- -if M-i E: -t :-r-- r:..r : -. . ml :'7.i- r: 

t-L- z: i: Ei-f if ua-; :: in n:ii^; r: vij-i 

- 

ID 

- ~ ii.: .-.-..- - ■ . - ~ - 
------ . Jk. year tuBb rnnmfi «tl i 

T.e~n. ~-; :i-*~L~: i :r ';it H'Th'T 

E r i -n : : ...' i : " -l .: ; : t_;. 

~i"f _i_ t_*'.i t .'":■_"- ^: ; .i-i ii.i" ^ r;L ~i:" t r: 



:>t ; ".:■: - ; r ... - 
iime v l: 

itsl'j r: sic - 

-'■ : r - ' 

7,'. T:_f _t - ' Ml' Mr 





- - - - 



gflwiBil 311 £helam& «ff m. 

:n ~ . ' M- r 



V Li MM - 

I 1 " M i ^ r . M r'M' 

."' . :.'!t "- i. ~i :m! 



one dtm- v 

I't r. ■. M- .It M M LI L. :Cl'f-"i •: Mr.; ". M! 1-Mr-f- 



mjf "niLT:Lnij£ citf: i)x&r:ef a: mt-sc 

M Llif ■ £T _U M'.'il ^t"; v. .1 •; ; r : - M.* 
'r' 7:." ; ii i i mii : t: [.: :-';.•;- ">: r' " • v ._m 




i l: l" M't f.ii: :j '"v" : M'.mi l: : 7 t >m m t-m 
: : 
sdEberthe otsert-ataans of etcher J^strnnomsrs Ts*r 

:■- ■:.<..- r m:_. Vr' . - ' - ~ 

- ' . - _ - M ^ : . 7 : ' :.:: .: 

- t - r inasmiiL': 

' " " . * — .m; : : - m - : 

- . . :>r l:t:.)I.m- 

_ . 

- 

~ .': ' 



Tf n:>£ : r." i :i:>i '. 

v" li; , r 7 - L " T Mf 



.ijiii a: iiijjetrtt ~akaffl^ 

. . m t i." ■: : - 7 M7':::' " 
Tit-ri-mrK indta f.ti r turT 



7l"eClf*-77: ; Mr 

n 



Astronomy. 



29 



/ 



which I shall be able to tell you the meaning of 
that term; for when we have measured the dis- 
tance ot the fixed stars it seems impossible to go 
beyond that distance accurately : Yet it is done 
approximately by this space-penetrating power of 
the telescope. 

If the pupil of the human eye could be expanded to 
twice its present dimensions, it would receive light 
sufficient to enable it to penetrate twice as deep 
into Space. It is found that it can now see a star 
of the sixth magnitude. But this does not give an 
exact idea of the space-penetrating power ot the 
eye, because the distances are not in the exact 
ratio to the amount of light. A star of the sixth. 
magnitude is twelve times more distant than one 
of the first. The human eye is capable of penetra- 
ting into Space twelve times as deep as the line that 
joins it to the nearest fixed star. If we could in- 
crease the diameter of the pupil and make it twice 
as large, it would see twenty four times as iar. — 
Now if we aid the eye by the telescope (it may be 
approximately done) how shall we determine the 
relative approximative power ?■ I answer: By the 
diameter of the pupil, or the object-glass, of the in- 
strument we can arrive at a very accurate measure- 
ment, with regard to that matter. Allow me here 
to make a very familiar illustration. Suppose upon 
a level plane, indefinitely extended, it would be 
possible to erect posts a mile apart. On each of 
these posts I will place a board which contains a 
sentence in a given-sized letter. Now the first one 
is just visible to the eye so that it can be read at 
the distance of one mile, but to read the next one is 
impossible. I, however, provide myself with some 
assistance. I take a telescope and find that with it 
I can jast read the sentence written on the second 
post. I take one with a larger object-glass and 
read the third : another larger still, and read the 
fourth. Thus I will always know the space- pene- 
trating power of the instrument with which I read 
anyone of the distances; and here is the principle 
— it is in this way we are able to penetrate from one 
to another depth, and to know what is the radius of 
the mighty sphere of which we are making an ex- 
amination. 

The first question is : Whether it be possible to 
penetrate through the depths of the Milky Way ? 
Herschel attempted this again and again. He 
takes a spot just visible to the naked eye, and with 
a low magnitying-power begins his examination. 
He finds this spot showing hundreds of stars, and 
behind them appears to be a niiiky whiteness 
which indicates other stars more remote. He takes 
a telescope of larger power and this causes the 
spot to blaze with more stars ; yet still there is a 
milky haze indicating that he has not yet penetra- 
ted the utmost depths. He takes another still 
more powerful instrument, and yet he does not at- 
tain the outermost limits, for still there is a haziness 
beyond. Finally he places his forty-feet reflector 
in the direction, and then finds the whole to glow 
with beautiful objects like diamond points upon 
the deep, clear vault of Heaven, without a stain 
beyond. (Applause ) Now he knows he has pen- 
etrated to the outside, and he knows how much 
power was required to take him there, for he has 
gone onward step by step till the last haze is re- 
moved. I have had occasion to go through the very 
same examination, and lean give not the slightest 
idea of the feelings produced, when upon opening 
the full power of the telescope, I looked entirely 
beyond the limits of the Milky Way and saw these 
orbs resting upon the deep, unstained blue of 
Heaven. (Applause) 

Well, now, what is the depth of these strata? 
We find it possible to guageit; we throw out the 
sounding-line, as Herschel calls it, in every possi- 



ble direction. He has done it, and the prominent 
part of this particular spot extends to such a 
depth that there must be a series of five hundred 
stars, one behind the other, and each point as re- 
mote from the other as is the nearest fixed star 
from us. Such is the depth of these objects. Now 
we are able to measure its figure and tell its di- 
mensions. This has been done. I will not delay 
the audience by going through any explanations 
of the manner in which it was accomplished. 

Having determined the figure of the Milky Way, 
the next point is this : When we stand out upon 
the outer circumference of this mighty circle, what 
is beyond? Is it possible there is anything be- 
yond? or have we reached the ultimate limit? I 
answer, we have not reached it. When we look 
out upon the heavens, we find not only hundreds, 
but thousands, ai-jd, with the aid of the telescope, 
tens of thousands of islands, all as magnificent as 
tbi3 mighty cluster with which we are united, 
whose suns number hundreds of millions. Now, 
can we tell anything about their distance? Can 
we locate them in strata, as we locate the stars 
belonging to our own System? I answer yes: it 
is easy to estimate, with a given-sized aperture to 
any instrument, how far it will discern a star of the 
first magnitude. In case it be removed till it is 
jast visible through the great fifty-four .feet tele- 
scope of Lord B,osse, it is ascertained that the dis- 
tance is so great that its light will take 60,000 
years to wing its flight to us. (Applause ) Re- 
member, this is one solitary cbject — a single star. 
Suppose it were possible to gather up the Constel- 
lation of Hercules, which is another universe some- 
what like our own, and so near to us that by the 
aid of the ordinary instruments it is found to be 
composed of brilliant stars ; let us move it back- 
ward and backward till the mighty eye of Lord 
Rosse's great telescope just loses sight of it. 
Where think you it will be ? I am almost afraid 
to tell you the distance; it actually overwhelms 
the mind ; it gives such an idea of infinity that it 
seems impossible to comprehend it. 30,000,000 
years will it require for the light to wing its flight 
before it can reach this Earth. (Applause.) 

Such are the distances we are permitted to pene- 
trate into Space. I have had the opportunity of 
examining a large number of these magnificent ob- 
jects with one of the finest instruments ever mount- 
ed. We find among them every possible variety 
of form. We find these clusters sometimes in a 
globuiar figure, occasionally forming a ring of light, 
as the Milky Way, and, in short, in every possible 
fantastic shape imaginable ; and still they are all 
governed by one Law — all subject to the influence 
of Gravitation, and their stability is perfect. 

I have spoken of the distance of the stars. I 
intend now to carry you along with me and give 
you an idea of the Periods of Motion among these 
mighty objects. We know that the stars which 
compose our own System are not fixed, but are 
moving, and we have reason to believe that these 
remote objects are energized by the same principle. 
We find, moreover, these mighty clusters seem to 
be scattered through Space not indifferently, but 
by a certain law. It is strange that a certain 
stream of them happens to occupy a position nearly 
perpendicular to the direction of the Milky Way 
itself. Now when we return home again and com- 
mence an examination of our own System, we have 
to start with more minute, smaller periods. We 
find among double stars some moving swiftly. In 
Hercules there 's one whose motion is so percepti- 
ble that you can observe the change after a lew 
nights. It performs its revolution in thirty-seven 
years only. There is another in the Northern 
Crown, which completes its revolution in forty-two 



30 



Prof. MUcAeffls Lectures. 



T33 7.33 73 33 : ~~' 3 1 :j it.: : 37 3 37- 
l Zi: :: _- _" 3 33 .3.33 :: T3£ I 33 -• 33 33 e 
is a qiLS-drnpie set, fenced by two seta of doable 
6 :--r; ; .3 ::' ::f-i 7 33 35 33 33 33 7.37 : ii- 
the oriber in two tboassna: jeara; ami, inasmuch as 
~z-z ~~- - - -' '■'-- -~ 3373 3 : --- '--•;=-" — - ~7i 
;:;£::e:::r:-e- : - ^ - "-- -' -- - : '' '-■ - \ '--: "•---"- 

re- 37 73 333 3 3: 33333 33 73:733 :: :~= ::" 
-._ T : 1 : ! - « £ := £ 3 : 3: 73 £ : : 7 1 : 33333 : : . : 3 77 33 

;;:-_ 3 33 " 3 £..~ = 7 33; 33 3 -I £ 3 - : 3 3 - : 7 7 3 .-. - -1 s 

": _: s-_i: is :_"-i ::r_;i:;:~._ 3 3 "=.:: :_•: ..: :: 

:_ 3£ 1 . - -£t ::' - = :~ :ei ii :_:• C 77 3733 :':e 
: Li-rL: I £73 373 ::e: 3 -i: *" :. 333—3. 333 
me bow it was that Miedler bad recently deter- 

:3.3_ 33 3:377333 3: 73 : 7; =—•: 53333. :_ 
t.3 3 fr: -r:= £3.3: ~. 1:1 3 ::tr,-- 3: 7333 : 77 
5-7 ::.<£ •' £ £ :::.:7:, 33* 77.:.=- '7.: 7 ::"..:7:7 
:;. *- ;. :_.7,_ -r :i7_ :: 737 33. 33.7 3733 3 
v-j ;e:-:r;:J: ;•£•:: 373 ris 333 £ .33 £7- 
7 3x33 £3. 3 35 3:737 7.: 37 3353 — 3 £ ; . 7: .3 = 
tl e :3 ;: .3 -33.3 s :7: ;:7 7: 3> s :: 7.7. ".1" ... '.'/. 
c: - £375 :•: :.77. -:f ::= ::::'. £.*••: 7: 77.= 337 333- 
737' 1: ;:£7 ^t 3333 :■: :£ 7 £ ::£ 3333 ::' 
E:r777:: 3£££35 33:37 35 3 sj.:.e 333:3 7: 
c:=7 3 -s'r. :: 3-33 :£•£ :: 7.33 I .7 It: 775 5377.33 

t_£ 173 373 7 337 -3 3 35 33 537! 3 ££ 777-.:£r3 33337 

tir 33333 ::' -.33: 3.3.3 3:7 -3-37 773: 5:333 

tI33 33 33-7 .733:5 13£7 5" ~~- 33 £.7 7 "_".".- 

; . ; ; ;•; :: ' th*s r: r.771: 33:33 33 5 31 3: ::ti 
studies his mighty jouroey. To bring tfcem all 

C£7£3 £§3-71 "3 71 -r £3773- 77£r:3=e Z-Isir.-I.. if '.'-t 

ratjo fa aay thing like what we suppose it to be, 

:=.>". 3- :it" s-£ r 7r-:.7:.;i :: : 77 . —3. :.- 33: 

S--3' ^7 ;:£-- 3£ :73' I7£T 373737 :7r3 :73tr3 ~ \._ ~t 

777373 -:7*_: .7-:^ . :; :: --.:; £-3 37:733:7; Zt37- 
77; 77 _;■•-.'. 33 :.:■£• - r r •- 3 73-3 3::.3_^ ::i-3 :_t 

37:33:-£r": -73.1— :!■£- - 3IT7 7t£7 

If there be anything;, then, that can lead as wp- 

•s-£77 ;.. :i£ :.3:-3 773 t7.:i : :' "=-. i::-: . ~ : -.z. 
-*-_; s7-T£7i- 3.. 7_33.3£ :; : 3- 33.:. :: ::' H.s _;■; -f. 
i::s:33 7.3.:-7£73_:.-3; :: t£ £ —1735 •.:•:-=■. l:'7i 

7T . _. ; .- _ . — }£ £ ^ . ' T337..77 :_£ "33 3 3 _ 3 33 • 

:t7 .:' 73 3, 3:7 si. £ 33i: : .-3t _:-:vt 37= V3.7 7 7 

tie 3 373 3 7' 3 333 33; ir';" - 3.3 * : £3 3:3 . .:±: 
D7 73t :31353_33-' l' :7'r7 s7;T333£ 3 37 _ 3 7 £ £33 
c! 3333:3- --r 73.3..: _.3:i-7-33 I :' 7 73 -*■ Z 3 " 3 3 £- 3 

_.3 3r i : 333 I:t73::;. 7 _.-: :£.. t: 73.3- :: e :: ■ : t : 
773: 3. 73= _i -3: £: .33 -33 ;:;•£-:•;— 733 £t 

3 3£ 3t33 3 -. 3 3- 3 _£ r 3 £3:3: 3 3 3: 3 
7 3 37£ 3 : : 7 ~3 3 _ 3" 33 : -3 3_ 77 33; 3-7 

3337s: 333-3- 33-33 3333: :33s ££37 3 £3 7737 1 e 3: 
73 73 I.: 3 33:-£3::;333 37 3. .iTi3: 3- T333 
_33i-£:35 7? '333 3333 -__ 3 3 "- 3 Trr . ; ::T; 
___' :3t3 3' _7 3 337.333 33 3£ 3333 3:: 33" 
133-3 3_ 3 7 7V . _ 3 75 3 3 3 3: 33 rX33s£33 3 J35 
W7_ 7333 ': 73 *3 . 33 Z 33 3 . . 3. s 3 : ~ 1 3 

•eamparis-n with the UDiverse bat a grain of sand. 

!:'_.. 33 :7_£3.:£37 75 33: 337 333- 3 35 53733 
7.3.7 3333 33 5373. 3 333 -353L --7333 3 
133 33 £-3 £33 3 33 373 ■ 333 £:3_3 

to project this Earth, it eoold not more it throogh a 
single -hot in a thoasand years. Yet God has 

773 33 3 3 . : : : : --' 3§ 5 33 3 _ 33 ': _ 3-1 _; ___33f 
This is nothing. Bemember this, that sonae Al- 
mighty power is swinging not only this E ____u bat 

E-"tI_ r. £3375 .:' 37 .333 £: 3: 3333-33 :; 1 
3-3.335 3 .3- 33333 3 33 33 3 3 333s f 3335 
J_ll 33 33 7 3353 333 33 737337 33. 33 3 

6 3i£ -:::: 3:53: 3 3: : -33. .-3 5373 33 3: 33- 
ing their mighty revolatjons. If there be not a 

C.:-!-:: : 3 :■■ '. 733-.. 3 33 333 3 37 3 £ 373:3 
_3 3 7 33 733 33 3-3 3 7: 733333: 3 

.:.-_ ; ~ i 3 37 3 33 33 33737 3 ="3 ~3 3 
h£Tli_ 333 3 . r . 3 35 3.3-3 3 7 : 3 3t 77* 3 7 
333 33" 3:3 .£ 3 3 3 5: 3 33 33.3 



7 33 •" 337-37 3. 73333 33 733333 333-3:; 

33: 3J 3333 33 33-33333 ■: 3-377 373T 
333 3 -3 3 3-- 33333 :~ 3 33 33: 33- 
3333 3 3. 3 33373; "-3 337 3 7 3737 3s 
"3*7 3— 3.7 33.3 3 3 33.3 33i 33 3-' 
33 3 3 " . : ._ 3 5 : 3.333 33 377333 3 

33-77 . 3 ;• 3 : - - - 3 7 _ 3 -. 3 3' -333 

33.37 ■- - ' 73 3 3 .33-3 3 .:^r 3 : 7 337 

- 3 _. 3 3 : : 1 3 r : 1 r: _ 7 : : i 3 : 3 3 r 3 3 z 3 £ 

■ 3:3 3." 3 3 I ~ ' 3 . "*" t . 3 3 : 3 3 33_3 

7 3 3 3 ~ 3 3 7 r _ 3 £ 3 3 33 "3 3 3 33 3: 
-- _3 3 £3 35 5 I 33_3; 333£_3. 33; 

3 3 :3..-33 3 £_:-. -3 37 £3.7. 



- ' 



3 3373 I 7 377 73 3 
." 3_37- 337 3 33- .3 
7733 £3 33- I 3533 I ■ 

3 3 : : 37 : ^ 7 73.7.7 
Many of yoaii 
£3: -3-7 7.-3; 37 7 
: 3 • 3 5 3 : ■=" 33 £3 :_ 5 7 33 
:s 3: :: 3: I 333 333:3: 
mentisidle? Wbyisi 

33-3 5 3 33t7 13 3333: 
3 t 33.3-3 _ : 3 33 5 £3 3 
3-37 3333333 £733: 
33333 7333. 3 3 
3335 3 35 £ 337 33 

-5333 3 £3—37 3 7 

13 33 3-5: 7 £33 3: 5 
3 3 \ . ■ 3 3 £ 7 3 -7 3 £ £ 
3 3 3333 33 3 3' 33 3 3 3 7 
3 3 3 5. 333- £33 733 
733 333-3 33 7 33 7 

ments. t» erect the \m 
groazd, are not able to g 

£37" 

3373-33333373 

3 3 3 7-33. 3 33.3 
77 37 773733 33 £33 
5 3 3 3 7 5 1-33-3:33 
33 7 333 : 3' 33_7 3 
33^33 £73 3. 37 7:7 
33 3'3: 3:33 3 

am now before joa. I< 

3 7 '. £73 3 3 

33: "3- £373 7 3 33 3 3 
I 7 37 3 3 37-3333:3 3 33 

£33-3 : 3 3. . £ 3 . _ £" 

3 33333: 3. 33 3373 

of the eqaaaor. It will 

7 3:3 3: 3 3 _3:3 3 
33 333- . . £ 3 3 33 3-5 

may meet at. the eqaatn 

33 £333' 333 733 £7 
33373: 3 33 7333: = £ I 

3 £3-7: 737 3 35 7 335 ~ 33 
;33:..:7:3: 3 5 37 
l" — 33 3-3 33 3 ^7 3 333 
73 3 '■■ • Z'- 3. =7 : 
3£: Z 3£-£ £ 



£33377 33 3 
377 3 3_£ £337 
"33 3 5735373 3 £ 5 

£33 373737 3_£ 77. 
37 33 33333 33 
37 53373 737 3 7 5 
33335533 3 7333 

73£*. 

I 33 333 333. 
£ 33'*- 33 3 3333 3 



H 
3_ 37 3 
3 3 3 3 3 

— :■ : 3r - 

3 3 3 £ 3 3 



sympathies or feelings ; but should this periodical 
commend itself to you, it will be of course gratify- 
ing to me to have your aid and support. 

I cannot part without expressing my deep 
and sincere gratification at the manner in which 
you have, through storm and tempest, through 



Astronomy. %\ 

rain and sleet, through mud and mire, stuck close- 
ly to me from the beginning to the end of this 
Course of Lectures ; and I shall ever cherish with 
pleasure the grateful recollection of this, I presume 
my last, public appearance in the City of New- 
York. (Great applause.) 



, — - — 



A S _ 



B¥ ; 



_ 

Oil 



--=..-:-K ' .»- Z ZfitiZP'E £.£ 



<- 2C3 53" 16 1 £ * 



WITH ADDITION iXI RRECTH 

BY DE. LABI : 



" ~' - - . I_ 2 . _- I „-._"■ . .- ..-. 



: 



el: ezz : :. : : i : z 



' '7 ~* j"j 



1.1.71. t ; 






c c 

i z z~zz ~.z ' 

>--.iiii-L- l.i-v; :.,;' _t I.t:^:'-'^ : :' _ . i.' — > : 7.7-i. 

1,1 "Vi :i" Uit 7._t:r'ii i i I L-l — _ -"—--ri — ~: -"."■- 

- — — ." — 

— ~ Li " — _ - ~ — - — _ . — _ 

— — 






_ 



"__ 



V.UK ttBttTf 



- '. 
-i — . - — 



— " 



' — 
- 

— . : ■ " ■. - : — - _ 

' ;>ii: 7 t.-.-::-: : ;. ' .: Zumiira . ;:: : 7t"7-.. .- .._ j . . i. 

_ _ 7 LZTZ 
— 
\ ■ ■ — - 



— - _ — 

"_ 7 "," -.~ 777. 
: _..."_! — _ ._ - :..•: :iu : ._- Iu:~-i — 
- .'- i — _ ._~i.l_ ....; in i :7 int ~.r — 

— 
— — 

I ;. . • . " _ — I 

I t - :/-ii_;:-i : i : ■' " 

- 7, ■— r - jtt 

_ 1 : -. 771 -'" 1 r " r — . ; _: VZ. -1 !_-_"_. ~17 '- 7 — 

7~i . ZLl~ :-" II :oi. 

----- 

- - - ; 7 L-7 :n .: L7l 1 _ - _ . V - : _ .".- : . ~ IBJEBft- 



.:; I :. .:i ;.-_• 



r_i.: - 






: ;-. ; ■- ::'".' :mv: 7: _ 7 :•: - r — _ r zzi\ Lri ' : m l:~ : :' "_7 T"__'7-: : :■ r- :':>: : - 



LIBRARY OF CONGRESS 




003 537 161 8 



Hollinger Corp. 
P H8.5 



LIBRARY OF CONGRESS 




003 537 161 8 



• 



Hollinerer Corn. 



